Are you talking about the roms or the real thing? If you're talking about the real thing, the number one (and most obvious reason they even made X) is SLOWDOWN. Huge slowdown in 2, but you wouldn't know that only playing the rom.
X has more animations and more... well, a lot more of everything. I don't care for what they did with the introduction of the aliens way too soon. I love that you find out about the aliens at the end of 2. If it wasn't for the zombie dogs and no slowdown, I would say 2 kills X.
I still think 2 is better, if you play it one player and don't mind slowdown all that much. I will try to go over a few differences, however:
2: slowdown, X: hardly none
2: better colors
X: new announcer
X: new characters (barely)
2: a few thigns here and there were taken out from X. Big plane flying over head was taken out of X, right?
X: poor placement of bosses... so 2: better boss battles (IMO)
2 is of course more original, and overall a better feeling game. Better pacing, while X was trying to be a "turbo rainbow edition" and so they didn't care if they showed aliens and spaceships right away. You knew they were there, so why not go crazy. So... erm, "story wise", 2 is a better play.
Spike
