Just a real big improvement over the first game. Most especially improved is the single player, whose levels are now based around a wide variety of weapons which makes for a campaign with substantially more variety even before factoring in the more cleverly designed (albeit difficult) DLC campaign. The basic gameplay and multiplayer modes haven't changed much beyond the addition of a coop mode, but both still work very well. Inking paths then zooming down them is still novel as core conceits go.