Played both single player and coop. Liked single player, loved coop! I don't know if you intend to make some procedural generation, but it would sure make it a great party game.
I always love to dabble in a bit of procedural generation but I'd only ever add it if I didn't feel like the levels were too random. I'll have to come up with some mildly complex rock placement algorithm. Already made some more levels for after the rating period has ended. Thanks for playing!