Pretty great little co-op game. It's asymmetric multiplayer, so you and another person do individual puzzles and have to communicate to solve them. There are achievements for either side of the playthrough so make sure you play it twice!

We ran into a frustrating situation where the last achievement requires you to flip a bunch of hidden switches across the game. However we missed out on one of the last switches as we died in lava in the final room (because the devs have an elevator fake-out that drops you into lava) and it locked the door behind us, preventing us from getting the switch. This would require us to do an entire full playthrough again. Pretty bad system in this case.