First, this game was incredibly polished, so well done there! This was also a unique take on a tower defense that I could really get behind. Not having to think about the towers or their placement really put a bigger focus on the action, which is a nice change of pace for such a genre. I think my only critique would be that there is really no reason to save up on gold, as each tower costs 5 each time. Maybe a system where different towers cost different amounts, and triggering a tower with that amount of gold would place that kind of tower? Just a suggestion. That and upgrades to the ships gun itself would be fun, since thats where most of the gameplay is. Seriously though, well done!