Good!.
For some reason remember me to the GTA for Game boy Advance.
I think you could skip the first level to speed and damage, are to slow. The other things is this a "positive game flow" that mean the game become progresively easy, as you become morepowerfull, in a short run it's not a problem, but i would let the player unlock the keys earlier, if not when he get the second key it's alredy too overpowerd, it's likely to stop playing before that happen. I do soafter unlock the blue key because i feel like this run give me all i can give me, neither feel like play again as, there are no more strategy i can try in a new run, be easily solved with other weapons to try or a wide array of upgrades types, like armor, a shield that reflect bullets or simply be hable to close the doors.
These were more sugestion and posibilities, it feel satisfactory for what it a lastest.
But the camera movement and SHake it's pretty annoying, I get me a little dizzy.