I’ve played or reffed;
GURPS fantasy (nice characters, slow advancement, slow combat, massively DEX weighted. I’ve only played a little of this, just one or two short campaigns so my opinion doesn’t carry much weight, I’ve met plenty of people who believe it’s the best game going but it didn’t really work for me).
Various white wolf dark ages (pretty cool but felt a little odd, works better for me in modern settings).
Ars Magica (fantastic game, I haven’t tried either of the last two editions but the stuff I did play was brilliant. It helped that our ref was a god amongst GMs.)
Rifts (fun but totally bonkers. Not even a hint of party balance, my shephard went adventuring with super ninja death monsters and demigod spellcasters. But a good time was had by all.)
Rolemaster (death by tables. Too many charts and referencing different weapons against different armours against different weather on different days of the week. Total madness.)
Warhammer Fantasy Roleplay (We played this for years, an excellent, well balanced game with plenty of scope for playing ordinary people in difficult circumstances all the way up to world changing fantasy superheroes. The new edition looks to be better balanced and tweaked for better game play although I haven’t tried it. The main shame about this game is that GW stopped producing material for it and I don’t know how much support it will get from Fantasy Flight Games.)
Runequest/Elric/Hawkmoon (I ran this game for a couple of months whilst we were weighting for 4E to come out and it works very nicely. The combat is brutal and extremely cinematic (Plenty of arms and legs being cut off), the magic seems to work without being unbalanced and there are plenty of source books and ideas for it. The rules are tidy and it’s easy to improvise ways for dealing with unexpected situations.
However the biggest weakness of RQ is the company that makes it, Mongoose. The rulebooks are untidy, full of mistakes and errors, the print quality is terrible,even after they gave up on their own printing facilities and got them professionally done, the combat rules vary from book to book and overall the whole production is sloppy. The company seems to have a policy of telling the customer what they want to hear rather than what is actually going on and it’s worth checking out a number of reviews on each book before buying it as some of the books are a total waste of space (Eg Spellbook) and others are fantastic (Eg Bright Shadows).
That said it is a good game, after I’ve finished my 4E campaign I’ll probably run a game of Runequest again. My players seemed to like it and it was a pleasure to run if you want David Gemmell-esque heroic fantasy.
I hope that helps. These are only my opinions and different people like different things.