There are a few issues I have with this game.
1) The money system is practically worthless, I bought all of the weapons like 3 or 4 rounds before the end, I wasn't counting. I think it would have been more effective to allow the user to spend money on upgrades, rather than only getting 1 point per wave. As it is currently, you pretty much have to invest everything you have into one weapon.
2) The Sniper Rifle is way too overpowered, since even non-headshots will still almost kill enemies, even without damage upgrades. I think other weapons should be made more powerful for body-damage, and the sniper rifle should be for people who are confident in their aim.
3) The bloody screen effect only really works in FPS games, and even then it's kinda annoying. Especially when you have enemies spawning from the left side of the screen and you can't see them because the screen is covered with blood. It would probably be more effective to have a health bar at the top of the screen that flashes when it gets low, since alerting the player that they're about to die is important. I just think you did it the wrong way.
4) The weapon variation was pretty shallow. There was a pistol, a sniper rifle, and 3 automatic weapons that function at different ranges. How about shotguns for when a bunch get close? Or heck, maybe grenades and/or flamethrowers?