Man, I really love the concept of this. Controlling the two rocks is so much fun, but I'm really bad at it.
My dumb brain just can't handle whenever the arrow boulder is to the left of the wasd boulder, it makes the control feel unintuitive in that instance (for example to bring them closer together you need to push both A and ->, buttons that face away from each other). Not sure if this is something you should correct or just a problem with me.
Anyway it's so much fun to pull off those choreographed physics dances that let you accelerate to ludicrous speed (and likely die right after in a hilarious fashion xD). It's so much fun, I just wish I was better at it.
Also I managed to completely fly right over a checkpoint and die right after a couple of times. xD I'd consider making the hitbox for the checkpoint taller.