Thought I'd like but hated:
Dragonlance Saga. I don't know how many of you remember this one, but UGH. The diceless card system. We were playing in a Ravenloft campaign when this came out, and at the urging of our DM we converted our characters over to this mess. I was excited because I was playing a thief in a game where everyone goes up in level at the same time, and at a glance it looked interesting enough. Suddenly, my formerly-next-to-useless Thief became like unto a god because it was easy to manipulate that system. I thought they'd soup it up when they changed the basic engine for...
...Marvel Saga Rules Terrible. If you were creative enough, you could make any power do any thing. I was so excited for this one to come out, but the critiques above carried over.
Rifts Great concept, and I love the idea of the kitchen sink setting, but the execution was brutal and unbalanced.
Thought I'd hate but really liked
Changeling I couldn't wrap my head around it when I looked at the books, but when a buddy of mine ran it, I had a blast. The clunkiness of the oWoD system was still present, but it was a fun, imaginative game. Under a different Storyteller, the miles may have varied, however.