Damn, that was nice.
Only bad thing that I found is that my game forgot what stable frame rate was after the city part of act 2, luckily, I died after getting the SA Angel Island checkpoint and it got fixed, so.. Maybe you should fix that, I don't know what's causing it, but yeah.. Also, this is just a detail, but the tittle screen isn't right placed and you have a weird black border thanks to that.
After that little errors and the weird fact that a mini boss reappear a lot in act 3, that was really good, it was fun, it was fast, it was smooth, I don't understand why you have to end act 1 to unlock the other 3 chars, but that's ok. As I said, only real bad thing is the frame rate after the city segment, but once fixed, everything was just a fun & fast adventure