WISH: Game Systems
My thinking on game systems is that whatever system the GM is most comfortable with is fine by me. I would even play AD&D (a system I can't stand) if a good GM were running it. Who knows? Maybe the problems I have with AD&D stem from having really bad dungeon-masters.

Game systems that really work
GURPS- I've run several games in GURPS and the system is great for certain settings. The combat system can be as complicated or as simple as the GM wants and the GM can easily add or subtract as many rules as he/she likes. Character Creation is about as balanced as you can get. (The idea of a truly balanced game is the holy grail of game design. It's nice to strive for, but you're chasing a myth.) The detailed skill system allows for more detail in the all important question of "what can my character do?" Experience and character growth allows characters to grow at a fairly realistic pace while being able to gain new skills after each adventure. The game only breaks down at higher point (aka high-powered) levels as character creation becomes extremely unbalanced and time-consuming.

Champions- (aka Hero System) Champions is is a little heavy on the rules and unlike GURPs it isn't as easy for the GM to run without using all of the detailed rules. However, most of the rules are excellent and add a sense of depth to the action. Combat in Champions can really feel like the action in comic books. Comparing Champions to the other superhero games I have played is like comparing the movie Batman to Spiderman. Both are based off of comic books characters and are fun movies, but the action sequences in Spiderman actually felt like a comic book while the fight sequences in Batman were stiff and awkward. I've never used the Hero System for anything besides Superheroes, but I would think that it would also work well for a very-high powered fantasy game. Any low-powered game would probably be better off using another system, since Hero was really created for the superhero genre.

Masterbook- (the out-of-print "universal" system from West End Games) Masterbook included the Indiana Jones Roleplaying Game, Tank Girl, Necroscope, Tales from the Crypt and one of my favorite games of all time: Bloodshadows. The system was much more streamlined than GURPS or Champions. Character stats can be created in 10 minutes and still have a decent amount of detail. The main thing that I loved about Masterbook was the card system. At the beginning of each game, players were given cards that allow their characters to take special actions or in some cases be able to add their own sub-plots to the game. Also, Masterbook required very little dice-rolling. In combat, one dice roll would determine both if a character hits and how much damage the hit does.

(Coming up- Game systems that almost work.)