Customization options were cool. The menu style/vibe was pretty nice (I could tell there were some unfinished bits, but I liked the finished bits)
When the enemies get up on you, the shots don't do damage. Not sure if that's intentional or not, but if it is, maybe some sort of "error" type feedback to indicate they are too close. It also would have been cool if there was a way to get yourself out of the middle of them quickly so as to start doing damage again. The simulation mode was insane, but I thought it was fun.