Good game!
This was a fun little game - not too time consuming, but entertaining while it lasted.
The game could definitely had used a little more depth - turrets, factories, and power plants...and that's it. The upgrades and all weren't even all that necessary until the third level, which was far and away the best. The final level was also just a little too simple, hiding behind walls and ambushing the enemy while they can't touch you. Also, the pacing is a little weird...the first level is very easy, the second one VERY hard for some reason, the third one just right, and the last level a piece of cake.
The game sure looked nice, though, and the effort is there. Just more depth and variety, and this would be great.