Could be better
I don't know is it because I'm not a fan of shooting games or not but I got bored right after I max all the upgrades. There should be more things to it I suppose, although it seems you've put quite an effort on the designs of the ships & tanks. It would be better if you'll add the storyline into the game rather than putting it on Author Comments because I don't think many people would read it. That way, it would be more interesting.