I have played D&D 3.5 for years. I know the whole thing inside and out, so much so that my friends actually check with me before they check with a rulebook.
I have been interested in other systems, though, lately because of listening to the Brilliant Gameologists podcasts. Recently I checked out GURPS. I know that the system isn't balanced, but it does have one feature that I am enamored by:
The self-contained Skill Check.
In D&D, the idea is to roll higher than the DC for a given skill. For attacks, the DC is their AC. For skills, the DC is given in a chart and can be modified by situational penalties like tumbling through underbrush. For opposed skill checks, the DC is the opponent's skill check.
The system for D&D has 2 parts: getting your DCs lower or getting your skills higher. For most, that is a no-brainer. Optimizing a skill is simple: make your modifier so high that it is impossible to fail, even on a natural 1 (if you deem they are -10 like I do).
GURPS has a fascinating system that combines the two aspects of the D&D skill system to make the entire things self-contained! You want to roll lower than the "DC," to start. However, you make an unmodified roll to do this! Instead, all of you skill is stacked up on the "DC," all of your situational bonuses are added to it, your base stat that affects it is added to it, and any penalties you get are subtracted from it. It covers both aspects of D&D without being open-ended. You never need to consult a book or chart. Just roll under your personal "DC" after all modifiers, and you succeed!
For opposed checks, the person who beats their own personal "DC" by the widest margin is the winner.
That system has an elegance that I find fascinating. I feel that that would speed up play quite a bit!
What are the downsides of self-contained skill checks?
What are the benefits of open-eneded skill checks that D&D employs?