RPGs come in a vast array of flavours. Setting is one way of splitting up the flavour of RPG but the split I'm talking about here is more on the ruleset. I'm going to be very general about the terms I use here largely down to my blasé approach to rules in a RPG.
The level of detailed mechanics (crunch) in a game is normally one of the elements that a player looks at first before deciding whether it's a game they're going to like. I used to say that you can determine the complexity of a game from just looking at the character sheet and see how many boxes there are...
Yes the setting is normally what draws them to the game but mechanics are important; at least in the sense of what level of control you want over your game experience.
Over the past 10 or so years there's been an increase in the profile of so called "story games" where the mechanics are such that they are designed to drive the story in the game. Essentially these story based mechanics are to enable narrative control of the gaming experience rather than to be explicitly about achieving a task.
As I mentioned previously (way way back I think) I picked up FATE Accelerated Edition primarily as a pre-cursor to my anticipation around the release of the Atomic Robo RPG.
FATE as a system is mechanically different to what I am used to playing, it's also very different from what my current player base is familiar with playing and I suspect that for some that suspension of disbelief mechanically will be a challenge.
Within FATE the mechanic trigger of an Aspect is how a lot of abstract actions are handled mechanically. As is touched on within the FateRPG website these can be a direct replacement for a skill/feat/ability or whatever label is applied in other games, the key difference though is the abstract nature of how that aspect is perceived by the player and the GM.
e.g. Bland: Swordsman.
Tasty: Trained Fencer.
Bam!: Trained by Montcharles.
The equivalent in practically all versions of Dungeons & Dragons would be represented by level, proficiencies and other more objective and defined measurements. Being able to say that you're a 12th level fighter with specialisation in Longsword makes it sound like you're pretty good with that Longsword.
Saying that you were trained by Montcharles sounds cooler though!
Both approaches work it's just a question of what style of mechanic you want in your games.
Me? I'm mostly an objective mechanic player but that's probably more down to my analytical approach to things in general. The subjective approach doesn't give me that same level of clarity around what bonus the character gets. It does sound cooler though!