I love the concept... but the game has issues
Mainly, the amazing ease you can beat it. On the hardest level, simply upgrade to tanks and choppers. Put the game on fastest speed, and spam both as much as you can.
And that's it. They take care of everything, oftentimes winning you the round before the first enemy even shows up on your screen.
After about 5 minutes, I had ~$5 million AFTER I bought each upgrade (All of which are completely useless except for the artillery, which is very cheap and unbelievably useful). However, you don't need artillery, because spamming tanks and choppers insta-wins the game.
The art is awesome, the gameply is great, and the upgrades are interesting. Unfortunately, all of that is lost when the game has absolutely no strategy. You just click on tanks/choppers at full speed and the rounds are over before they begin. The hardest thing strategically about the game is figuring out how to click fast enough to keep up with the build speed.
If the enemy had more units (say, AA guns that were only susceptible to marines), and you got far less cash for killing people, I think the game would be great. You should see a tank or two, and maybe 1 chopper in a battle. The rest should be utilizing your strikes (which should be nerfed and made cheaper so you call them more often, seeing as how they're fun and dynamic), and trying to outsmart the enemy, not out-spam them.