A Small Glance to Xanathar's Guide to Everything!
New content? On this guide? But of course!
Xanathar's Guide to Everything is essentially the first book on the (very small amount of) D&D 5e Content that is explicitly meant as a player-centered splat. (Sure, there's Sword Coast Adventurer's Guide, but that's mostly a campaign-related splat, and Volo's Guide to Monsters which is more of a "Monster Manual 2".) The biggest part of this book is the huge amount of subclasses for each class, which naturally includes Paladins. It also includes a lot of spells (of which Paladins get only a few), and some common magic items (as in, literally of common rarity). It also makes tools a bit more interesting to use and gives some sweet downtime applications that are better than those explained in the DMG, but...that's best kept as a side benefit.
First, let's go to the meat of the book, and what you're waiting for: the subclasses!
Oath of Conquest (LD): The first of the new oaths, and another one that's pretty dark. Basically, your purpose is to enforce order through fear, and much like the Spanish Inquisition, fear is your main weapon. Mostly, you can play it as a dour officer of the law, or a brutal tyrant. Usually the latter.
Channel Divinity - Conquering Presence: Creatures within 30 ft. must succeed on a Wisdom save or become frightened. The frightened condition is pretty nasty, since it imposes disadvantage on attack rolls and ability checks, meaning your enemies can't hit you as well as they'd want to. It doesn't require concentration and you can hit them without losing the condition, but they can negate it with a saving throw on each of their turns. Good luck following them, but later on, you get a sweet ability that helps you a LOT.
Channel Divinity - Guided Strike: Got Great Weapon Master? Wish to hit with that sweet, sweet +10? Here's your chance! This is identical to the War Domain Cleric CD, by the way, but you get only one use. Use it wisely, but when you use it wisely...you do remember that you can stack up your Divine Smite WITH your Smite spells to go hideously nova.
Aura of Conquest (LD): Remember what I said about the frightened condition and "good luck following them""? Well, if they're frightened within your aura, all of a sudden they can't move. What better Lockdown method than this? Well, what about the DoT effect dealing psychic damage while frightened?
Scornful Rebuke (DR): Alright, so if they can't move away from your spot, and they can't hit you that well, right? So, what if they STILL manage to hit you? Well, that's when you punish them with psychic damage! Do note that it doesn't consume your reaction, so it applies to EVERY ATTACK MADE AGAINST YOU! ...Dang.
Invincible Conqueror: Alright, so - the oath itself is pretty good, but this capstone is just absurd. Resistant to ALL damage? Three attacks per round!? IMPROVED CRITICAL!? Yeah, it lasts for 1 minute, but compared to other capstones, this is probably the best capstone ever. Bar none.
Oath Spells: 3rd - armor of Agathys, command, 5th - hold person, spiritual weapon, 9th - bestow curse, fear, 13th - dominate beast, stoneskin, 17th - cloudkill, dominate person
Tenets: Beat them until they cry, punish rebels, and if someone's stronger, follow them until you can prove you're better. In other words; you play the bully. It's hard to play this and be non-evil (or non-chaotic), but if you're Lawful Evil...you pretty much do this already.
Oath of Redemption (DR): AKA, the controversial Oath. See, if you ever had access to the Book of Exalted Deeds in 3.5, you may remember Vow of Peace and Vow of Nonviolence; ways to play a non-violent, pacifist character. You may also remember that there was a LOT of heat about it, because all characters are glorified murderhobos. Well...this oath requires you, and empowers you to, not fight. I mean, you *can* fight, but the idea is to solve things passively.
Channel Divinity - Emissary of Peace: A nice, non-concentration based buff to Persuasion checks. It's a solid +5 bonus, and lasts for 10 minutes. It may seem real, REAL bad...but Persuasion is a strong weapon. If you manage to get a HUGE result, that person can be persuaded (pun intended) to agree with what you want. This power is as powerful (pun intended, again) as how much you can get from Persuasion.
Channel Divinity - Rebuke the Violent (DR): Someone hits an ally of yours, and does a bajillion points of damage while at it? Spend your reaction, cause the target to make a Wisdom save, and deal either a bajillion points, or half that amount (and half a bajillion points is still large enough). Do note that it works only once per short rest, and it's either this or EoP, and which one is better? (Hint: probably this one.)
Aura of the Guardian (DR): Remember the Crown Paladin's Divine Allegiance? Well, this is infinitely better; it affects creatures within 10 ft. (and eventually 30 ft.), so you don't have to be close to your target to use this. However - this means you either use this, or Rebuke the Violent. Noticed that your reactions are being assailed a lot?
Protective Spirit: Basically, Survivor for your character. When you take all that damage, you need to be able to survive, no? This gives you 1d6 + half your Paladin level, so it's between Survivor and using Healing Surge every turn. (For comparison: at 15th level, that's 1d6 + 7 HP, which is close to 10 hp; in essence, the same amount of healing a Champion with 20 Con would have. This gives you a LOT of survivability.
Emissary of Redemption (DR): The capstone. You get resistance to all damage from creature attacks (Sweet!), and if you get hit, you return half the damage you take (remember you're already resistant to all creature attacks, meaning you deal about a quarter of the damage), which applies EVERY TIME. Did I mention it applies EVERY TIME? Because I forgot to mention that this capstone is ALWAYS ACTIVE. You're right. This is the ONLY Paladin capstone that's always active; rather than having a time limit, the effect ends if you do something? What's that something, you ask? The reason this isn't the best capstone, like the Oath of Conquest capstone - it ends on any creature you harm, by means of an attack, a spell or an effect that causes damage. Note that the retributive damage doesn't count. Ask if stuff like Shove and the Shield Master's bonus shove action to knock prone don't count as attacks (note that they don't do damage, and you don't make attack rolls with them), and you can keep enemies locked near you. Just...don't do opportunity attacks. Like, ever. It's not a bad capstone (far from it), but it's hindered by its absurd restriction.
Oath Spells: 3rd - sanctuary, sleep, 5th - calm emotions, hold person, 9th - counterspell, hypnotic pattern, 13th - Otiluke's resilient sphere, stoneskin, 17th - hold monster, wall of force
Tenets: Here's where things get rough. The tenets all but force you to be a pacifist, by making violence a "weapon of last resort" (meaning: it's not your first course of action; you instead attempt to pull off a Persuasion check), leading by example and being patient (aka, turn the other darn cheek!). Of course, the last tenet gives you a slight excuse to fight ("...Well, the enemy won't stay its blade, and my people are pretty much dead if I don't act!"), but it won't always work. Thing is, it depends on the kind of campaign. With a good DM, this won't be much of an issue, because that good DM will always allow you to gain XP and defuse fights through talking. Most DMs, though, force you to fight monsters, and spending the first minute trying to stop them from fighting will be both impossible and a cause of grief. That said: I had a real bad experience with Persona games, and Redemption doesn't allow you to negotiate for XP and treasure, and most veterans won't accept playing with an actual pacifist, so I place this on a bad note.
Ceremony: You get a set of cool rituals that require an hour to use. Note that atonement, once the Paladin's ticket from being a glorified Fighter, exists in a way here; you can use it to negate the effect of a helm of opposite alignment, if you want to. You also have an excuse to Bless Water as a spell (though you still need to spend the powdered silver). However, the cooler ceremonies involve a 1/lifetime guidance effect for an entire day, a 1/lifetime bless effect related to saving throws for an entire day, the effect of gentle repose (corpses can't become undead) and/or a 1/lifetime (or until widowed) fixed bonus to AC for an entire week while close to your beloved one. Alright, so they're cool, but their benefits are extremely limited (I mean, once per lifetime!?). Note that you can create holy water through a ceremony without casting the spell (see the PHB), meaning you don't have to memorize this spell. Let the cleric prep it instead.
Find Greater Steed: So, remember find steed? That awesome spell that lets you get a beefy steed? Well, this lets you get flying steeds! Or steeds that have better stats (like awesome dire wolves!) Sure, it's a 4th level spell, of which you have a few, but a spell that grants permanent flight or an entirely new and useful character to fight alongside you? Priceless.
Holy Weapon: Ah, a classic! You can enchant your weapon to light up as a torch, deal some SWEEEET radiant damage (2d8? Nuts!) and your weapon becomes magical if it isn't already. But, did you notice that, as a bonus action, you can basically do an area smite!? Wait: AREA HOLY SMITE!? Seriously!? Wait; IT TAKES A BONUS ACTION TO CAST!? Forgive me for this, but I'm sweating like a horse after seeing this spell. Good lord, Holy Weapon merged Holy Sword with Holy Smite and made it a super AWESOME spell! It's a 5th level spell, but...then again, it's a sweet 5th level spell with a bunch of benefits. (Trivia: Clerics also get this spell.)
New Magic Items
Let's face it; pretty much all of them are redder than the burning rage in my soul. Mostly because their effects are meant for fluff. Some of them could be considered decent.
Clockwork Amulet (THF, Arc): 1/day, make an attack as if you had rolled a 10. If you know you're gonna hit on a 10, this is perfect. This is ALSO perfect if you have GWM or Sharpshooter, because if you can hit with a 10 despite the penalty, that means you ensure one attack. Mix that with Divine Smite and whatnot, and you end up with a perfect tool for a nova-based class. It doesn't require attunement, either!
Mystery Key: You have a 5% chance to open any lock. ANY lock. That means you have a 1 in 20 chance to open magical locks, complex locks...pretty much anything. Try it on any lock. They're common items, so they can eventually be purchased for very, VERY cheap.
Rope of Mending: You can cut up the rope and then mend it again, as long as the bits are in contact with each other. This kind of item rewards the smart player; find a reason why to have a rope that mends itself is useful, and exploit it.
Ruby of the War Mage (THF, Arc): Your weapon becomes a spellcasting focus. You already have holy symbols, but this means you no longer need them. You still need to have a hand free for somatic components, though; do note that, if you wield a weapon in two hands, you don't have to always have them grabbing the weapon, making this perfect for fans of these weapons.
Walloping Ammunition (Arc): On a hit, target must make DC 10 Strength save or be knocked prone. In your case, that means your subsequent attacks will suffer; on the other hand, if you have a lot of melee allies, that means you give them advantage. Knocking prone is a pretty solid tactic, and you can find several ways to reduce a creature's saving throws. After a while, it won't work anymore, but keep a handful of them, particularly if a bard is close.
Bountiful Luck: Remember the Halfling's Lucky racial trait, that lets you reroll 1s? This lets you give that benefit to an ally, but you can't use Lucky afterwards. The range is 30 ft., but it's a really potent boon that you give.
Dragon Fear: This lets you have a secondary "breath" effect, allowing you to frighten enemies. If you're a Conquest Paladin, it's great. Otherwise...it's cool, but not that much. The frightened effect ends on a successful save, which is made every time it takes damage. Decent, but not excessively impressive.
Dragon Hide (US): Basically, you turn your Dragonborn into a poor-man's Monk. The claw damage is pretty decent, but you can wield better armor anyways.
Drow High Magic: At-will detect magic is fairly good, but the other two aren't so much. Plus, are you seriously playing a Drow Paladin? ...Eh, can't blame you.
Dwarven Fortitude: Interesting power you get; you can spend one Hit Die on a Dodge action. So, when things get dire, you can heal AND impose disadvantage on attacks. Pretty sweet, considering that you might not get to spend those Hit Dice as you gain levels. Note that Half-Elves get access to this. (*wink wink*)
Elven Accuracy (Fen, Arc): Ouch. This feat is absurdly great for Archers, because that means you can reroll your lowest attack roll if you have advantage. Also works for spells, but few (or actually, none) of your spells require an attack roll. Also; remember that weapons with Finesse key off Dex.
Fade Away: 1/short rest, go invisible after you get hit? Sweet, but this is awesome for...Rogues, not for Paladins. Unless for some odd reason you REALLY need to Disengage after attacking.
Fey Teleportation: Gain misty step, as the spell. It can be useful, as it's a 2nd level spell, but a) requires you to be a High Elf (generally not a good idea) and b) it can only be used 1/short rest at most. Not good, but not bad either.
Flames of Phlegethos: Searing smite is a thing, you guys. Also, hellish rebuke, considering you need to be a Tiefling. The "reroll 1" effect means you deal a bit more damage, and the wreath of flames is rather decent. Cool, flavorful, but it depends on you spamming searing smite, which won't help you that much.
Infernal Constitution: Gives you a free set of resistances and advantage with poison, which is pretty cool.
Orcish Fury: Just when you thought your smite couldn't deal more damage, you get one damage die. Wield a greataxe? Congrats; you just dealt 2d12 plus all your smite damage. And in case you dodge death, you get a free attack with it! As racial feats go, this one is pretty solid.
Prodigy: Expertise as part of a feat!? Who doesn't like that? Couple that with a skill proficiency, a tool proficiency AND a language, and it's a great package. It works for humans (pretty common), half-elves (very good) and half-orc (pretty nice!).
Second Chance: Get a free reroll 1/short or long rest to an attack an enemy makes. Decent, but not very impressive considering you're gonna get hit a lot. At least it gives you +Dex, +Con or +Cha with it.
Squat Nimbleness: Hey...you a Dwarf? Surprise, you're no longer as slow as before! Gnome or Halfling? Why, go ahead of course! Goblin! ...I think you actually go faster! You also get a free skill proficiency (with Acrobatics, even! You know that there's only ONE background that gives that proficiency?), and advantage on checks to avoid being grappled, which is pretty nice. Nice, but not overwhelmingly good.
Wood Elf Magic: Alright, so playing a Wood Elf isn't exactly conductive to a Paladin, but at least it lets you get a druid cantrip. Get guidance, and exploit the heck out of it. Longstrider is also super useful, because it extends your movement speed.