This game may be nothing special but its fun gameplay and story suck you in for hours and hours. Did i mention mayhem?
The gameplay is pretty straight forward: Collect Brains and destroy everything. The you go that pretty much sums it up. First of all this game is a 3rd person shooter, and its just flat out blowing crap up. You harvest brains from humans and you caan also brainwash them and other cool stuff the farther you get in the game. You also fly in a flying saucer and you blow up whole towns, yah its that fun to. You also have cheesy but somewhat funny scenes where you take over a humans mind and fill in words for them. Its just lots of fun and theres plenty of guns to feed your destructive side.
The story is just you being an alien and needing brains, not much else. You might as well leave this alone if your looking for a lenghty in depth story (although the later in the series you get the better it gets).
All in all Destroy all humans is great. And its title explains it all, destroy as many of us as you can. Sounds lovely doesnt it?