Well, lets start from the obvious, this game is a clean hit, nice graphics (for an alpha) an good thought out movement of the tanks/sprites.
Now to the critique and ideas!
I thing the bullet time is a little bit confusing, ok it is nice that i can turn it off, but I think It might be better to start as off on default, or even better to give it only on the last kill!
I like the levels simplicity and they work quite well, have in mind that after I died a couple times in a row from a new comer with invulnerability, I tended to mask my tank behind obstacles.
So you have to expect heavy camping taking place in the game. You might thing something that will force someone to camp less.
One thing is the delay between shots, great idea but it is a little confusing as to when you are ready to shoot again, maybe a loading bar on the tank will help that.
A possible power up will be faster loading for example!
An the thing that I didn't like was that I could see the spawn point of my enemy, that gave me an advantage, even though he has the shield.
Do you considering diversify the spawn points? Ok its a small level but you may add two, three more and random spawn on one of them the next player.
Overall a great game with very good potential. I really like the explosions and the graphics.
Also, the name looks good, I like it!
I'm looking forward for more updates!