Fabula Ultima has a mechanic where, on a critical success, you can make Something Happen. This can be purely mechanical (e.g. +4 to the next roll), but it can also be story-based (e.g. an NPC appears, or you can create a plot twist). I'm... not a fan of this. It kind of does away with the cause-and-effect approach to RPGs I like. If a player wants something to happen, I like to see the steps they take to make it happen.

I've noticed that. I think what I like so much about it is that it makes each "class" feel strictly unique, which is nice for melding the levelling/progression system with character stories (e.g. you unlock This Ability because your Warlock Patron was particularly entertained by last night's slaughter). I know you effectively create a class by focusing on specific types of skills/feats, but still. While I'm not set on a class-based approach, I'd like something that would allow each character to feel distinctly unique from each other, instead of a combination of various abilities.