By shooting monsters Player earns money to buy new weapons. Completing levels or playing survival mode earns EXPERIENCE points, that can be used to improve the main character's abilities.
Controls:
WASD - move
MOUSE - aim and shoot
E - place mine
SPACE - go to shop
Okay, but...
The core mechanics work fine... nothing really new, but the controls didn't bug out on me, either. On the other hand, I stopped playing the exact moment that I realized it didn't save my money or my guns from previous stages. Players like that sense of progress, of getting steadily more and more powerful as a game goes on. When they suddenly find out it's not there (at least in any lasting way), it's a big letdown.
Not bad at all
At first it looked crummy, but it was interesting to play. Faster bullets would be nice. Various shot sounds for each type of gun would be good. Having permanent upgrades for a high price would be fantastic. You've got a good structure, just needs some more work :)