It's a cool concept, and you did a great job with the visuals, but there are a couple things that kept me from really enjoying your game. The block placing was a cool idea, but it was a little finicky, especially since you could only move it once. Several times this led to me placing down a block too low or too high and having to start over, as well as accidently releasing the mouse and having the block be stuck there. Also, it was unclear where to use the blocks, and i died more then once because i fell down a pit that you need to place a block in, which wasn't immediately clear. Also, the enemies often came out of nowhere at high speeds and cost me a life, and I gave up on the last part where you need to switch your gun to kill the corresponding enemies, because you can't see the enemies until it's too late and there's no time to switch. I did like the ideas you had, and I feel that with a little more refinement, you'd have a pretty solid game.
P.S.
If you wouldn't mind, I'd appreciate it if you tried out my game and gave me some feedback