Nice concept, this could be a really good game if was put more work on it!
There's a list of thing's that could be improved:
1- When you are in a corridor, you can't avoid enemie's bullets.
2- The game has no instructions about the controls. It's easy to figure out, but it's always important to remember to tell the player the controls.
3- It's possible to pass a level by outside the screen.
4- You don't know how much life you have left.
5- The covers in the middle boss won't protect you well.
6- The bosses could have more health.