Would be nice if there were an option to turn down the music; listening to music while playing is out because of the background music. Otherwise, the game is good!
First of all, the game is a lot of fun, molto bene. Here's some ideas and things I've noticed that you could add or change if you plan on working on another sequel. Have you considered upgrade-able towers? Could add some more strategy to the game. Possibly to draw more interest from people who haven't played the previous versions, design your maps off of places or cities in the world to have a sequel were "the creep invades Earth." I like the idea of the storage buildings but, they may be more useful if they themselves stored the extra energy. This would allow you to build them farther away from your base so energy gets where you need it quicker making them more useful while not eliminating the need for speed buildings. Last but not least, possibly something for a further future game too, have you considered multiplayer? such as having one player be the creep and instead and a fight to the death instead?
Anyways, just some ideas for you. Keep doing the good work!
For the sequel you should add a trophy or achievement system. Us Kongregators like to accomplish stuff!
All in all though it's really a great game, awesome upgrade system, small map but it plays really well. Well done, 5*!
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