Difficulty. Took too long to make a sequal (just kidding).
I remember playing the original TM way back in the day, so it's a treat to be able to revisit those good ol' days with a new version. It's similar to the original in many ways (which is good) and really should make all of its fans happy. They've also added new characters and weapons which just adds to the anarchy.
The story mode follows 3 characters - Sweet Tooth, Mr. Grimm and Dollface. The story is decent, but I was very impressed with the cut scenes. They were very well done and were almost movie quality in my opinion. As for the different stages - they consisted of killing everyone, kill everyone and stay in a moving zone, races and boss type battles. Most of the stages were fun considering it's a game about shooting at cars/helicopters. My only gripe was that even on "easy" I found it to be very difficult and it took many tries to finish a few levels. I don't think I'm terrible either, so I can imagine a lot of people getting frustrated with the difficulty settings.
The multilayer is the main reason to get this game though - with up to 16 players in a match it is absolute mayhem. Bullets and missiles are flying at you constantly, but it's a ton of fun. It's one of those mindless, go balls-to-the-wall type of games where you just want to kill anything and everything.
Overall, I was very pleased with this game. It was a long time coming as fans have been harassing them for years to make a sequel, but I think they did a fantastic job. Fans of the original and newcomers should really enjoy this game.