This was sooo fun! :D I was pleasantly surprised! Took a few tries on medium before I made it, and then I also managed to beat it on hard. ;D I think the slight recoil when the tanks fired was at first a bit unsatisfying because it sort of wrecked the ability to make nice formations, but when I'd played a few minutes I realised that was actually a really challenging mechanic in a good way! I liked the inevitable chaos. Balance-wise, there was no real need or practical purpose to mix up the tanks. I used mainly orange ones with some yellow ones mixed in when there was a spot behind the orange ones. I also made heavy use of the bombs in the two last waves, perhaps the bombs were a bit to cheap in contrast to the gain of using them. When the enemy was packed in the last waves, it was easy to drop the most expensive bomb on them, because it paid itself and another bomb for the blood money.
There was only one thing that disturbed me a bit, and that was the fact that the buttons did not always respond. Even though I had the amount of money to buy another tank, a few times I had to click a fair bit of times on the icon to get a new one. Perhaps there's some cooldown involved, and if so, I would've loved to have a visual representation of it.
Another thing that would've made it reeaaaally awesome would be to map the tanks to keyboard numbers, to quickly set out tanks.
In summary though, sooooo good jam game! :D