Shadowrun for me. I've run it exactly once - I had what I thought was a cool concept for a short campaign, but I hadn't banked on (1) my players knowing
much more about the quirks of the system than I did and (2) their tendency towards power-gaming.
It took us hours to get through character creation, and about half an hour for me to realise that it just wasn't going to work.

Oh well, you live and learn.
So I did my reading, got excited to play, etc. The GM even let me play a werewolf PC at the start, which I thought could be pretty awesome. Got my PC created and we started our first session.
The rest of the players had a Glitter Boy, Juicer, etc. And I had this PC who at best might be able to do 1d4 MDC while everyone else was going crazy.
The one and only time I played Pathfinder felt a lot like that. I had a character that was actually pretty good, all things considered. Unfortunately, the DM was of the school that accepted anything that felt cool, even if it wasn't balanced, so all the other characters were comparative gods. In particular, there was one guy whose character could do
everything mine could do, but better. Oh, and he could fly, too.
(The difference, I think, is that RIFTS had that stuff baked right in to the rules, whereas this case was about the DM selectively disregarding the rules.)