I tried our Survival mode, which is pretty groovy. Starts off regular and slow but speeds up as you go along. After so many dudes you will go into a mode like the light saber/nunchuck rounds where you will randomly kill white dudes to give bonus health back, and getting hit in this mode doesn't take off your life. That way you can refill your life and keep on going.
I don't know if you need to hit a certain threshold or something but I got 1339 kills and unlocked Blind Survival mode, which is survival but the left-right indicator is hidden. Gotta gauge when to make your hits and those multi-hit pattern dudes are much harder since you can't see the pattern. Better know them by colors or watch how they move!
I got 800+ in that mode, which unlocked THE GREATEST BONUS MODE OF ANY GAME EVER! I won't spoil it, and don't you spoil it by looking it up on youtube or whatever. Just play some survival rounds and play it yourself. You MUST see it.