As we all come out of the catacombs, blinking slowly at the unfamiliar light ...
Actually, what I look for in a game system these days is simplicity. My philosophy is that, when *any* conflict or significant decision point comes up, the players and I should be able to roll dice, quickly determine the outcome of that round or that skill use, and move on.
I wrote an article at my website on a few "light" systems I liked. You could start there. I've never actually played Heroquest, Fudge, or FATE, yet, but I've played the others at least once.
Once I GM'ed GURPS (everybody groans), and I like the system. It has a reputation for complexity, but most of the complex bits are *options*, which means that you can play without them (unlike d20). Look at the free "GURPS Lite" version, which strips the rules to a playable bare bones.
I've also played older editions of Runequest, Call of Cthulhu, and a few other "Basic Role Playing" variants. It's a very flexible system, and apart from needing a character sheet listing *all* skills it's fairly simple and straightforward. You could also look into the Mongoose edition of Runequest, which is (a) in print, and (b) evolves the system slightly (with a few undesirable mutations).
Recently I ran a PDQ-based game, and apart from the over-complex damage system I grafted onto it, it worked out surprisingly well. Mine was homebrew; I'd suggest you start with Truth & Justice (superhero), Dead Inside (modern dark fantasy), Questers of the Middle Realms (satirical heroic fantasy), or the recent Zorceror of Zo (fairytale fantasy).
Some other games that look interesting, but which I haven't played yet:
- True20 (a simplified d20)
- D6 Adventure/Space/Fantasy (I'd suggest getting *one*; the others are mainly retreads of the same mechanics, with different slants and slight renamings. "Adventure" seems like a nice compromise, but if you're committed to Fantasy or Space go for it.)
- Savage Worlds (faster dice mechanics than GURPS, but "universal" in similar ways.)
- World of Darkness (Vampire, Werewolf, Mage, etc. ... kind of pretentious to me, but others swear by them, and the core book could form the basis of a "humans against the darkness" campaign.)
If you'd like to venture further afield -- as "Burning Wheel" and "The Riddle of Steel" indicate, you could consider these:
- Primetime Adventures (your game as a weekly TV series)
- Dogs in the Vinyard (haven't read yet, but it's gotten a lot of buzz)
- The Shadow of Yesterday (only skimmed)
PDQ is also a significant departure, but it's such a simple system you might at least take a look at it.
Actually, here's a belated question: what are you looking for? An interesting background? Simpler mechanics? More realistic mechanics? A better combat system? A better magic system? A system for capturing social dynamics?
"On two occasions I have been asked [by members of Parliament], 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question."
- Charles Babbage (1791 - 1871)