I really want to like GURPS but every time I try to actually play it, it falls flat on its face. In theory, having a completely generic, modular system should be a GM heaven, but somehow it makes characters and spells feel really amorphous, and the combat aspect of the game - again, very likeable in theory - is a pretty fickle thing.
For me, GURPS always failed at the "Generic, Universal" stage- too many alternate rules for things like psionics in various settings.
In contrast, HERO has never failed me, and I find Mutants & Masterminds an elegant hybrid of HERO and D20.
However, I've never felt like characters in
any universal system were amorphous.
Games I wanted to like more than I do:
I always wanted to like the 1Ed WoD games, but hated that they weren't in a single unified system- I always wanted my Mages, Werewolves, Vampires and the like to be able to encounter each other...
RIFTS was another game that I always wanted to love. In the end, though, the clunky mechanics forced me to abandon the game, but I keep mining the setting's fluff for campaigns in other systems.
Space: 1889 was very well researched, but its mechanics are also clunky. Again, its a game I mine for ideas more than actually play.