So, a little bit of catch-up:
Local co-op (up to 4 players: 3 gamepads + 1 keyboard) has been implemented, but the devs say in order to add online co-op they'd have to almost completely redo the game so that's not going to happen. The new class (#3) is the Bandit, who specializes in bombs and high-powered guns. I've updated the OP to be a little more informative now that RoR has become somewhat more of a respectable game, as well as added the details for each class (including the Bandit, so if you haven't seen his abilities check them out, Lights Out is pretty crazy).
From what I've seen in the beta (through streams from Northernlion and DeliciousCinnamon), there are several new items and the Monster Log has been implemented since the alpha/demo build.
You've got until May 8th to back the Kickstarter; $10 for the game and $25 to get beta access along with it. I'm in, so I'll be updating the thread whenever the beta gets updated. The devs have said they plan to release the first beta build right when the Kickstarter is finished.