Great Game! I would suggest that the enemies bullets don't pass through the crates, I hid behind them thinking they would stop any bullet, but then they went through and I got shot!
Also, tell me there's nothing in the upper-right there when the rock is done rolling. I tried at least 10 times to get up there, without getting killed by the rock, but couldn't. God I hope there isn't a secret room there, I'd be so pissed.