I'm probably being too picky about this, but what has always kind of bugged me about Mission:Space is the backstory. I think it's dumb that the "adventure" is that you're in a training simulator. I just don't get that at all. To me, the huge appeal of Disney is the escapism and getting to pretend. I would much rather pretend that I actually AM flying to Mars than pretending that I'm TRAINING to go to Mars. That one I just don't get.
I also don't like the time it takes to sit through the warning videos. I always find it distracting that it is very obvious Gary Sinise is reading from cue cards or a teleprompter.
Aside from that, I like the ride itself.