Theres so many things wrong with this...
First off' and of course- The levels were the worst effort I'd ever seen. Hardly anything to fight on even when you make your own.
2nd- Please for the love of god- Take out the fall through walls move! Or at least make it so its only with thin walls. Because you can hide in huge bricks (your own levels) and stand invincible forever.
3rd- The hit damage and recoil is crazy. It doesn't matter what gun you use- if your hit, your flying. I feel like a bunch of Sumo Wrestlers shooting rubber bullets.
4th- Speaking of guns, Its incredibly rare to pick up a gun you've bought. I played for half an hour and never even saw my shotgun or machine gun.
5th- It be nice to add in a HP bar along with trying to stay on the level. Cause this kinda defeats the purpose of deadly weaponry..
6th- Add some background at least. Looking at grey blocks all day wants to make me rather pay a visit to my grandma than admire your "hard work"
7th and Final- the game was addicting! Now i add that as a problem because, Being as horrible as i made it seem, I played for almost 2 hours straight. NO GAME THIS BAD SHOULD BE ADDICTING! this shows you've got potential. You just need to get your ass up and work a lil harder.
I hope you take some advise from me and other people (if any)
And I do hope you create a remake of this. Despite it's bad qualities, this could really make one awesome game.