Bottom line...fun.
Once I got my way over to the multiplayer, I haven't gone back to the single player. Multiplayer is set up very well on PDZ. It is customizable and varied. I don't want to get flamed for saying this, but I prefer this multiplayer over Halo 2's ten fold. It's vastly superior in my opinion. There are numerous different game plays and customizable elements with a big online community. I just am hoping for more maps and character skins down the line.
Bottom Line: The gameplay is very good. I've been itching for a solid FPS and that is just what I got...how sweet the satisfaction of getting and headshot. The multiplayer is some of the best I have ever player. If you love FPS, get this game! Oh, and don't come in to it with expectations. Just play the game for what it is, look past its flaws, and have a blast! This game is just plain fun.