Quote Originally Posted by olskool View Post
My favorite resolution system is actually a pair of systems. The first is the roll-under percentile system as done by the Design Mechanism's MYTHRAS rpg. You add to characteristics scores from 1 to 20 together to get your base skill before training. You then roll under to succeed. However, there are varying degrees of Success. Rolling under your skill is a Success but we break down the level of Success as follows. Please note that I "homebrewed" the Degrees Of Success to avoid doing math during the game.
Hard to beat percentage based roll under for maximum transparency and ease of use. Mythras wins in this regard because it is such a well-written system and I like how clearly abilities and skill values interact. Definitely one of the best. The most fun of this are the combats: when every successful action offers the opportunity to manipulate your opponent, hurt him in creative ways or gain some sort of tactical advantage. There are so very little things in a combat that are as rewarding as punishing an attacker for daring to strike at you incompetently and let them pay the price.
Here is an example of a duel run in Mythras, action-by-action, accompanied by a neat little short film presenting the fight.

However, my personal favourite is the old(ish) Cubicle 7 Doctor Who System (haven't played the new edition, can't say a thing about it): You roll 2d6, adding both a Stat and a Skill, both roughly ranging from 1 to 6, to the total result, trying to beat a target number, the higher the result the better. Again, super easy, very intuitive, and non-gimmicky (I don't like games trying to be clever and failing more or less spectacularly at reinventing the wheel). The fun part about the system is that the degree of success is well done, effectively adding the simple words "and" and "but" to the simple yes or no question of "did you succeed?", with a lot of free narrative space for the player to come up with these factors, not just for spectacular successes, but most importantly for setbacks.

Let's say, you try to repair the O2 recycling plant sabotaged by a mysterious foam monster on your moon base under siege. You roll on Ingenuity + Craft to jury-rig a solution, against a difficulty you might or you might not know. On a great success, you get a result of "yes, and...": Not only did you repair the recycling system, saving you and the cosmonauts from a grisly death by suffocation, you also found a clue about the foam monster's hideout!. A normal success ("yes") simply allows you to repair the unit. A marginal success, or "yes, but" would also allow you to repair the dang thing, but at a price: probably your loud banging has attracted the foam monster to your location - and know it hunts you through the dark corridors!
On the side of the success spectrum, you also get a marginal failure, or "no, but": While you couldn't repair the recycler (and the rest of the scenario will run under a ticking clock, until air will run out), you have at least located a weak spot: the foam monster is averse to great heat. Maybe you can use that in a later confrontation. Besides a normal, plain failure, however, you also have a critical failure, or "no, and..", indicating not only that you failed your task, but somehow made the whole situation worse: The O2 recycler might be still broken, but now also releases another gas into the station's atmosphere that makes everybody dizzy and intoxicated (fortunately for you, this might also affect the foam monster).