Yah, what he said...
Gets boring very quickly. Whoever wrote this probably doesn't like to play defensive games very much. Needs a pause button, and better music. Although you can toggle the music off by pressing "m", it needs it in an options bar. The power bar having to recharge all the way is rather stupid, and the clones are the same one or two thingies. Upgrades don't seem to make much difference, and if you buy a health upgrade, you should be able to get a full health bar out of it, especially when you are at full health when you buy it. Having to upgrade your health bar, and then fill it back up is pretty pointless.