I went to VC2 from VC1 so to me it felt like a big drop in quality, people like to talk about the story but that's something I could ignore. The smaller maps (with loadings) completely change the dynamic of the game, certain classes become too overpowered because of this, and it also broke up the pacing of the maps.
Also filler content, you were constantly replaying maps in VC2, and you had to do a bunch of filler-missions to advance on the main story and unlock new maps.
VC1 on another hand was new map after new map, I don' think there's a single obligatory mission where you play the same map twice.
Don't get me wrong, the gameplay itself was still fun, but it felt like a really harsh drop in quality, and repeating the same maps killed the game to me.