This was pretty fun, and the art works well. Definitely could use some additional mechanics. Zhong317 had some good suggestions in another comment. I'd also love to see some sort of progression mechanic; maybe you can buy/find weapon upgrades, traps, grenades? Also my tactic was always to strafe around the perimeter shooting inwards, and that seems to work well. (At least until I ran into some sort of invisible wall on level 4 (top left I think?) Maybe some sort of mechanic that interrupts that tactic so players have to change it up a bit.  Cool game though, nice work!

I like this visual style, a good prototype. You can consider adding more elements, such as:

• Fast-moving enemies.

• Add petrol barrels to the scene to guide players in a more reasonable position and deal a wide range of damage.

• Airborne medical kit or more powerful weapon, etc.

Nice game, remind old  Alien Shooter game.

Well done!
It's crazy like Serious Sam :) 

Nice top-down shooter, reminded me of Alien Shooter.

I think that there should be a compass to guide the player towards the exit, that way the player wouldn't stumble around blindly.

I like the "World-War 2 era" aesthetic.

All in all, good work on your first game.

Neat atmosphere! The dark levels looked good.