The gameplay feels pretty smooth, I even played multiple rounds. But I'm here not for compliments but for feedback sooo....
- Gameplaywise it only lacks content. Maybe drop more metal at the start of the game, for the player to be faster with his first upgrade. But besides that it feels good.
- Consider making an online highscore. It's not that much work and brings a lot to those highscore arcade style games
- Polishingwise:
- A backgroundmusic would do a ton
- Die sounds for the zombies and gethit sounds and feedback for the player
- maybe for the graphics saturate active objects more or the backgroudn less, to make it clearer to see in such a fast paced game.