Very happy to hear the game is fun =]!
There is no download exclusive content, everything will be available for browser. You can unlock tower 3 and 4 by beating level 2 and 4😉👍
Each boss have some tricks to beat it. The way to beat boss 2 is to constantly walk in circles around it. With just enough distance to avoid most barrage missiles and to keep attacking it. And when the nuke timer gets to 1 second, you dash away with space key. I´m planning to keep the game on the challenging side, but I´ll consider balancing it if it is too unforgiving.
Lots of good content to the game is coming hopefully this weekend, game will be updated weekly or so.
Thank you for playing🙌