Good game, but quickly runs out of steam.
Well coded, nice graphics, good selection of weapons, and the game presents a decent enough challenge during the early stages. That said, the game runs out of steam after 15 minutes or so. The first few stages will have you scrambling like a maniac, trying to defend your base against hordes of monsters with some pretty puny weaponry. But once you buy the Laser, the Overkill powerup, and boost your base's HP to about 2000, the game is basically over. You can literally ignore your base for the entire level, pick off enemies with the laser at your liesure, and watch the XP roll in. You can easily rack up 100,000 XP in one round that way, which makes the 1500 cost to repair your base a trifling pittance.
I'd like to have seen some kind of continual challenge, or reward for buying every item in the game. Perhaps the ability to upgrade individual weapons to improve specific stats, or some kind of boss monsters or something. Because once you get your HP and Base HP up to the 10,000 mark, you can even revert back to your original pistol and still come out on top.