So far it is definitely the campaign! The single player vs. the AI is pretty cool. I don't know if I like the fact that you cannot choose your difficulty anymore though. I saw that in the beta and just don't know if I like it. I definitely like the leveling up system as well. I like being able to gain levels based on my play, the only problem there though is that it doesn't require skill to level up. As long as you play you will gain rank.