This doesn't make sense:

[Jon talks a lot]

Why is Great Weapon Fighter so much better than Great Weapon Master?

Great Weapon Fighter states:
When you roll a 1 or 2 on a damage die for an attack you make with a melee weapon that you are wielding with two hands, you can reroll the die and must use the new roll, even if the new roll is a 1 or a 2. The weapon must have the two-handed or versatile property for you to gain this benefit.

Great Weapon Master states:

On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
Before you make a melee attack with a heavy weapon that you are proficient with, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attack’s damage.

Rerolling all 1 and 2's on your damage dice seems ridiculously good to me. Getting a bonus action attack when you score a crit seems...not. The -5/+10 is awful in tier's 1-2 when you aren't going to have a very good attack bonus anyway, and it's even worse in tier's 3-4 when 10 damage is basically nothing. Even at level 20, Great Weapon Fighter is going to feel awesome. Grear Weapon Fighter? You are going to wonder why you wasted an ASI on this.

Speaking of ASI's, the cost of great weapon master is far more than great weapon fighter. Great Weapon Fighter costs your fighting style, but if you want to use a two-handed/heavy weapon, the only other fighting style even in competition is defence, which you can take at level 10, assuming you are a fighter. Master, on the other hand, requires a feat, and while this isn't as much of a cost to a fighter as other classes, is still very expensive. You are essentially trading potentially a +1 to attack and damage rolls or an extra hit point per level or a +1 to a save/ability check for Great Weapon Master, and, as I've already shown, it just isn't good enough. I mean, people go crazy over getting a +1 magic weapon in their games, and increasing your strength by two is essentially the same, albeit not overcoming nonmagical resistance.

I just don't get what makes GWM good, and I often see people saying it's far superior to GWF. I do not understand.

[gloryblaze]

GWF takes the math on a d6 from (1+2+3+4+5+6)/6 = 3.5 on average to (3.5+3.5+3+4+5+6)/6 = 4.167 on average. Double that for a greatsword or maul and you're looking at 8.33 average damage per swing instead of 7, so a +1.33 difference. That's worse than the flat +2 bonus from Dueling, so it's not very impressive in the long run.

GWM, on the other hand, can give Big Numbers when combined with advantage or to-hit bonuses, like Channel Divinity: Sacred Weapon. There's tons of math done on the subject by other people if you wanna check it out.

[Snails]

Regarding GWF, it is good, but it is really no more good and no less good than is appropriate for Fighting Style. Employing a 2d6 weapon, it raises average damage by 1 point. I think that is fair when compared with Dueling, which raises damage by 2 points for the S&B fighter.

To be more explicit:
Base 2H avg = 7
GWF 2H avg = 8
Base 1H avg = 4.5
Duel 1H avg = 6.5

Seems reasonable to me.

As for whether GWM is good or bad, it is not so good that it should be applied mindlessly for most PCs. Yes, it can make you worse off. But, practically speaking, the key is to get Advantage on your attack by some means, and then applying GWM is a very good bet.

[Jon talks a lot]

This seems to be decent advice. The idea is that advantage negates the -5? Leaving you with a flat +10 to damage.

Advantage also has the advantage of making crits more common, meaning the Bonus action attack triggers more frequently.

I understand this a little better now.

[quindraco]

This seems to be decent advice. The idea is that advantage negates the -5? Leaving you with a flat +10 to damage.

Advantage also has the advantage of making crits more common, meaning the Bonus action attack triggers more frequently.

I understand this a little better now.

Also, and this must be stressed, GWF fails to scale with additional damage dice (that is, it scales to 2d6 weapons, but it won't scale to, say, Hunter's Mark).

The math on the Piercer feat is... really messy, and one of the reasons for this is that it absolutely scales with more dice (it also scales with bigger dice!). That said, the Piercer feat really demonstrates one of the key flaws in GWF: if you sneak attack with the Piercer feat and a hand crossbow, to keep all the dice d6s, you can pick any 1 out of the pool to re-roll. That's so much better than only being allowed to re-roll the damage dice from the weapon.

If GWF let you re-roll any of the attack's damage dice, like Piercer does, rather than only the weapon's damage dice, that would be a game-changer and we've have to completely reconsider it as a fighting style.

[Jon talks a lot]

Also, and this must be stressed, GWF fails to scale with additional damage dice (that is, it scales to 2d6 weapons, but it won't scale to, say, Hunter's Mark).

The math on the Piercer feat is... really messy, and one of the reasons for this is that it absolutely scales with more dice (it also scales with bigger dice!). That said, the Piercer feat really demonstrates one of the key flaws in GWF: if you sneak attack with the Piercer feat and a hand crossbow, to keep all the dice d6s, you can pick any 1 out of the pool to re-roll. That's so much better than only being allowed to re-roll the damage dice from the weapon.

If GWF let you re-roll any of the attack's damage dice, like Piercer does, rather than only the weapon's damage dice, that would be a game-changer and we've have to completely reconsider it as a fighting style.

Oh crap, how did I not realize that. That changes quite a bit of my analysis. It only works on the weapons dice, not on the attacks dice. Duh.

[MoiMagnus]

This seems to be decent advice. The idea is that advantage negates the -5? Leaving you with a flat +10 to damage.

Advantage also has the advantage of making crits more common, meaning the Bonus action attack triggers more frequently.

I understand this a little better now.

Yes, GWM only really works if you have a reasonable way to have advantage or a bonus to hit, but it's more common that you might think if the remaining of the team work for it too (Help action from the wizard's familiar, bardic inspiration, hold person, etc).
Without it, it's still a very effective way of dealing with lower level enemies, and since they're likely in great number, dealing with them effectively is quite important.

[RogueJK]

The -5/+10 is awful in tier's 1-2 when you aren't going to have a very good attack bonus anyway, and it's even worse in tier's 3-4 when 10 damage is basically nothing.

Not so. There are numerous ways to help mitigate the -5 penalty, even at low levels.

For example, Bless is an extremely common party buff, is a 1st level spell so is available from start, and will halve the GWM penalty on each attack on average (+2.5 being the average of +1d4).

Similarly, Advantage helps to overcome the -5, and there are quite a number of ways to reliably achieve that even at low levels, from low level class abilities like the Barbarian's Reckless Attack, to low level spells like Faerie Fire and Sleep, to easily achievable conditions like Prone, to a party member's Familiar using the Help action. And that's just scratching the surface.

+10 to damage on each of your attacks is still a noticeable bonus, even into Tiers 3 and 4. There are few ways to achieve such a large numeric bonus to each damage roll, even at higher levels. And even if you have access to other ways to add points of damage, they can stack with GWM. Thanks to the bounded numbers of 5E, each +1 makes more of a difference than in prior levels. In prior editions bonuses were handed out like candy and it was not uncommon for even low level characters to have +10 to stuff, but in 5E, +10 is comparatively huge.

[diplomancer]

Oh crap, how did I not realize that. That changes quite a bit of my analysis. It only works on the weapons dice, not on the attacks dice. Duh.

The RAW is ambiguous on that, but that is indeed the RAI, as confirmed by Sage Advice; still, ask your DM about it.

[Eldariel]

Regarding GWF, it is good, but it is really no more good and no less good than is appropriate for Fighting Style. Employing a 2d6 weapon, it raises average damage by 1 point.

1,33333... is the DPR increase for 2d6 weapon: you only get one reroll so the damage dice are (3,5 + 3,5 + 3 + 4 + 5 + 6)/6 = 4,166666666666666666666666666666... average each for a total of 8,33333333333333333333333333333... for two which is exactly 1,33333... more than for one die. It's just a bad fighting style and you should always take something else: Archery is about +4 (from Sharpshooter), Dueling is about +2. Defense, Interception and Blind-Fighting are a bit different: Blind-Fighting is Advantage at will for certain builds (so worth a ton) but useless otherwise, Interception and Defense run on different metrics because of how AC scales in efficiency depending on how close to getting off the dice you are, and because Interception mostly has party utility. Oh yeah, and Throwing is +2 too. The problem though is, said two-handed weapon means you don't have a reliable access to a bonus action attack which means your overall DPR will lag hugely behind anyone with it (dropping enemies and critting from GWM are not reliable triggers so you'll get those pretty rarely).

Get this: you're using a heavy weapon to deal damage. You give up your off-hand and ability to use Dex for attacks (while Dex is largely the superior stat to Str, affecting Initiative, a more important save, Stealth, etc.) in exchange for damage but then the one-hander gets all the damage back just from fighting style while you get crap-all. Archery does the most damage due to the best fighting style followed by GWF (without the fighting style: you generally just ignore it and use a glaive with PAM + GWM) and then Dueling PAM (which does surprisingly decent damage with the off-hand attack benefitting of Dueling bonus as well). Dueling PAM is actually competitive with GWM + GWF + Greatsword against high AC (18+ around late Tier 2 and early Tier 3, which certainly occurs - CR7 Dragon already has 18 AC) targets, because GWM falls off around there (and of course much earlier if you do get the reaction attack), while also getting a shield.

We don't talk about TWF, Protection, or company: those are pretty sad.

EDIT: Derped the numbers, somehow put Greatsword at 7,5 base instead of 7.

Yes, GWM only really works if you have a reasonable way to have advantage or a bonus to hit, but it's more common that you might think if the remaining of the team work for it too (Help action from the wizard's familiar, bardic inspiration, hold person, etc).
Without it, it's still a very effective way of dealing with lower level enemies, and since they're likely in great number, dealing with them effectively is quite important.

Also Barbarian, Battlemaster's Trip Attack, Samurai's Fighting Spirit, there are plenty of Str-melee options that give you advantage. Though obviously, lacking access to hit boosters and Elven Accuracy combined with more reliance on base dice makes GWM less able to utilise the -5/+10 than archery (which can basically always -5/+10 at profit due to the fighting style even without advantage, and gets stupid amounts of damage with advantage due to Elven Accuracy).

[Jon talks a lot]

The RAW is ambiguous on that, but that is indeed the RAI, as confirmed by Sage Advice; still, ask your DM about it.

I will. If the DM allows it, GWF becomes much better.

[Man_Over_Game]

Just to clarify, GWM, assuming your normal average attack deals about 10 damage, and you only need about a 7 or an 8 to hit, GWM adds about +2 damage to your attack rolls. With Advantage, double that bonus.

As your base damage decreases (like if you dealt 1d4 instead of 2d6), or as the enemy AC decreases (so you only need a 6 instead of a 7 on the die to hit), the amount of damage GWM gives you goes up, and Advantage basically always doubles that bonus (so if it gave you +3 without Advantage, you're getting about +6 with it).

That's why people like to combine it with PAM, since you get that extra 1d4 attack that's really efficient with GWM. It's also why Rogues should rarely get Sharpshooter (since they have a high base damage and thus have more to lose).

Maths: https://rpg.stackexchange.com/a/76656/45619

In fact, the benefit from GWF actually lowers the amount of value from GWM, since you're essentially increasing your base damage (causing you to lose more damage when you do miss due to the -5), while you lose nothing if you had chosen to get more AC instead.

[Willie the Duck]

I will. If the DM allows it, GWF becomes much better.

It does, but there's still some limits on how many extra damage dice one can find for two-handed heavy weapons. Smiting paladins and sneak-attacking rogue with revenant blade and double-bladed scimitar* can get some impressive numbers of dice, but in general I find them appropriate to the opportunity cost.
*not sure this would work, anyone know?

[RogueJK]

Smiting paladins and sneak-attacking rogue with revenant blade and double-bladed scimitar**not sure this would work, anyone know?

The Double-Bladed Scimitar does Slashing damage, so it can't be paired with Piercer.

[Theodoxus]

I will. If the DM allows it, GWF becomes much better.

Anecdotal, but as a DM I've always allowed GWF to be used on all dice rolled for the attack. With Piercer, I personally think there should be an new errata for the PHB that clarifies things like this, updating old phrasing to reflect the new. So that new published abilities aren't just defacto better than core.

Basically, update GWF to read as "When you hit a creature with an attack made with a two-handed melee weapon, or a versatile weapon used with two hands, and roll a 1 or 2 on any damage die, you can reroll the die and must use the new roll, even if the new roll is a 1 or a 2."

[TyGuy]

JC's reasoning for gimping GWF makes me roll my eyes so hard I strain myself. I see no reason why dueling with a shield should out damage GWF.

[Kylar0990]

Yes, GWM only really works if you have a reasonable way to have advantage or a bonus to hit, but it's more common that you might think if the remaining of the team work for it too (Help action from the wizard's familiar, bardic inspiration, hold person, etc).
Without it, it's still a very effective way of dealing with lower level enemies, and since they're likely in great number, dealing with them effectively is quite important.

Using GWM if you hit 2 out of 3 times you would have hit without it, the +20 form the 2 attacks you hit likely did more damage than the one hit you would have gotten without it.

[BloodSnake'sCha]

It does, but there's still some limits on how many extra damage dice one can find for two-handed heavy weapons. Smiting paladins and sneak-attacking rogue with revenant blade and double-bladed scimitar* can get some impressive numbers of dice, but in general I find them appropriate to the opportunity cost.
*not sure this would work, anyone know?

Don't forget the Flamethoung great sword.
And spells like hex/hunter's mark and spirit shroud, holy weapon.