Best graphics of any flash game Ive ever seen. An all around solid game. If this game was on a console id be pleased to play it as i have fire emblem, disgaea, and final fantasy tactics. That being said, its too easy. The addition of defense mode is great, however i found it possible to lock down an entrance grate with a single unit with an assault rifle. Then I just sat around waiting for the heavy marine to show up. 4 guys, 4 or 5 grates, and you can easily lock down the entire map, without a shot being fired. The addition of a hard mode, or even just increasing enemy HP would make this more challenging, and more enjoyable.
Im with the other posters, being able to purchase more weapons and armor would be great! In general more content for a game this awesome would be appreciated by all of us, keep up the good work.