Great game! The controls are easy to master, and the gameplay is quite satisfying. Although you said you did not spend much time on it, I think you have done a good job.

Well, all in all it's pretty fun, simple. It did get quite boring after some time though.

Having to wait to shoot is not fun.
Some weird bug makes me teleport backwards when shooting sometimes.
It lags bad sometimes.

Generally I'm not a fan of game that require you to grind in order for you to beat them but in this game not that much grinding is required to unlock every tank. I don't know if there's a max level to the bonus energy and health.
I don't know if you're supposed to use a specific tactic to beat the boss. The first three times it just ran me over.. the next time I destroyed it in seconds.

You could add some powerups to pick up in the arena.
Some nice metal music would suit it very well.
What is the end goal? How do you really win? There isn't any hint of progression or completion, objectives or direction (in the game). Also I think there could be levels with specific challenges instead of a single room and upgrades significantly affect difficulty.
I understand if you did this in a rush and don't really have time to add or adjust things.

cute concept and art, but the game itself is pretty lackluster. the tanks are difficult to control, and its very easy to die because of this. but it definitely could be fun with a bit more work!!

A basic, but pretty fun idea. Arrow-key controls as an option would've been pretty nice - WASD's pretty awkward for me.