World Tree . . . succeeding TOO WELL on a skill check can have unforeseen consequences. Not only did you beat the threshold, you beat it by 30 or more. The example given was of a singer entertaining a crowd, who gets potentially unwanted attention from a female in the audience. I like the idea that succeeding by too much can also be bad.
That reminds me. I have to change my answer again, in favor of streamlining.
Favorite single game mechanic is that outcome resolution rolls have only three results: favorable, tie, and unfavorable.
It's not the false dichotomy of succeed/fail. You don't either reach the top of the cliff or die trying. Your too-low roll could mean you reached the top, but in an unfavorable amount of time.
There's no reason to spend time adding up various bonuses from across the character sheet to get a better result; high enough is high enough.
No five-result-table is needed for every different type of roll, depending on how close you were to the target.
Mathematically, it pays respect to an important consideration: every result on the die has an equal chance of popping up. So you're not penalized for rolling too low on a one-die system, because the lowest roll has the same chance of occurring as the middle result. This is in contrast to a bell-curve system, when you have worse odds of a very low (or high) result, and high odds of a middle result.
A tie outcome removes the problem of "was I supposed to equal or exceed the target?" It opens up the possibility of an ambiguous outcome, or simply allows for a re-roll to determine favorable/unfavorable.
But if you REALLY want to say that something awesome happened because you rolled high enough, roll again versus your previous result. If you beat that, yeah, you got a critical hit or some other cool outcome. This effectively gives you the chance to do better when the bar is set lower - it's easier to get a critical hit on a goblin than the elder black dragon.
Disclaimer: I won't try to take credit for writing the only-three-outcome rule because much like fiction, every rule has already been written. Right? But there are definitely some rules I prefer over others ; )