Wanted to Love, but Hated:
GURPS: A universal set of RPG rules? Sign me up! I really really wanted to like GURPS, but it seemed to include almost every game mechanic I hate: hex-based movement, one-second combat turns, an ads/disads character creation system. My one caveat is that the historical sourcebooks have excellent fluff.
Aria: Canticle of the Monomyth: Again, great idea -- you get to play an entire culture, zooming in to the level of an individual hero, or zooming out to focus on the development of the culture as a whole. But, oh my god, did these guys like creating New Terms for Everything. Heritage Template, Reaction Orientation, Status Archetype, Developmental Window of Opportunity... and that's just in the character creation section. I've worked as a bookkeeper, I've done taxes, hell I've written a few RPGs, but I just could not grasp these rules -- although I'm sure they made sense to the people who wrote them.
I don't really have any in the other category -- who plays a game they think they're gonna hate? Life is too short, my friends.