I found Fez to be completely over the top complicated. I can't imagine the nightmare of completing that game without any sort of guide.
I greatly enjoyed Limbo. I kind of wish the No Point In Dying achievement was for no deaths instead of less than five.
I got Castle Crashers at launch (long before I cared about achievements) and I'm somewhat embarrassed to admit how many hours I sunk into that game. I completed normal mode with every character (in order to unlock all of the unlockable characters) and took a few all the way through Insane mode, which was quite a slog. I also found
a funny glitch. I definitely got my money's worth from this one.
I recently bought Shadow Complex on sale but haven't played it yet. Soon!
I'm a bit strict with my ratings, so I just looked at how I've rated my XBLA games- only one 4 star (Portal: Still Alive), several with 3.5, a bunch with 3, and some with less than that.