It's okay
Well, overall, Overrun 2 is a pretty good game. I haven't played the first Overrun, so this isn't a comparison. The only problem was the game got boring quickly. There just isn't enough variety to keep me interested. The enemies just seemed to differ in health and position and there was only one weapon (not including the room-clearing weapons). There just isn't anything to hold one's attention that long.
However, that isn't to say the game's bad. In fact, it was pretty good. The graphics were good and the sound/music was great. So, there's just that one problem impeding the game. Besides that, a good game!