Hated em, loved em
I thought I would hate the old TSR Marvel Super Heroes RPG. The class ranks (incredible! unearthly!) seemed childish even in middle school. But the mechanics move so quickly, everything resolves so smoothly. I've still never played a faster combat system, ever. And if you got the Ultimate Powers book, you were set with just about every power you could possibly imagine. (Dragon mag had a few they left out, but still)
Out of nostalgia, I picked up the newer Marvel "RPG" if you want to call it that. It sucks. Period. It's a low-end board game at best.
Cyberpunk 2020 seemed like such a cool concept when we bought it. I never did figure out the rules to make PCs in that system. Just too cumbersome.
Unlike everyone else here, our group is warming to GURPS 3rd ed. We're playing a steampunk game in it, and actually like it. Oh, so far we've avoided the advanced combat rules. Perhaps that'll make us hate it. But we kind of like having a few disadvantages on the Char sheets.
I used to love D&D, but have burned out on it. I'm just tired of the logical holes in the engine. Everything is combat-focused, so if you want to play a character-based game, things don't make sense. We quit playing 3.5 when two of us got tired of defending it against questions like, "Why is 'Create Musical Instrument' a lower level spell than 'Bless Water'? Shouldn't it be easier to say a few words over the jug than to create a complex, working instrument out of nothing?" I mean, the questions are legit if you look at it logically.
I played D20 Star Wars for a while and liked it more than I thought I would. I liked the idea of Fatigue and Wounds instead of base hit points.
I like Shadowrun until one gamer goes into the Net and suddenly everyone else at the table is on vacation while that gets resolved. And I've yet to get the magic and sci fi rules to blend smoothly.