I too greatly enjoyed this one because, though I am a fan of the X films, I recognize that they are extremely cheesy and full of cliches that make them ripe for the riffing.
I too have found it useful to break these up, if not over a few nights, but to take short breaks in the middle. The signal is when I'm no longer laughing very hard, I'm starting to "get used to it." The great thing about MST was that it was broken up for you, and it was only, what, 70-75 minutes movie.
I can't help loving:
"I'm in"
"She's good"
"you have no idea"
"wow--a superhero cliche hat trick!!"