OMGF GODLIKE FOUNDATION!
This game is incredibly well-concieved! You have such a great concept, that it practically blows my mind with all the possibilities for expansion/improvement!
Like everyone else is saying, I see this game as more of a great foundation for what may potentially be the greatest game on Newgrounds! As someone else suggested, if you make the bubbles into more of a type of currency, and start giving the player branches to the main tank's development (I.E. you could focus more of offense, defense, or speed/stealth/versatility. weapons could be similar; one branch could be like slow and powerful, another fast/accurate/homing/spread, but weak, and another could be sorta a middle ground; perhaps a small spray w/ bigger bullets than the weakest. Aaaaanyway, all-in-all, this is a GREAT concept with awesome physics engine + controls, ultra-dynamic concept with the world/overview, incredible potential with enemies + arsenal (the biggest bummer was hitting the final upgrade and realizing that I was stuck with one big bullet, and one little bullet... coulda been a better final), but yoU DEFINATELY NEED TO EXPAND THE GAME 1000-FOLD! MAKE IT THE GREATEST GAME ON NEWGROUNDS! YOU CAN DO IT, I'M ROOTING FOR YOU!