You could play it till the cows come home! A very entertaining game to play and observe.
You play as a little Alien called Crypto (I think) who's soul task is to go round various towns sucking out villagers brains, using your telekinisis powers to launch objects, fire your gun at everything, set fire to the buildings in your flying saucer and probing people. Basically causing as much destruction as you possibly can. However if you actually want to get somewhere in the game, you do have to play quite tactfully keeping a low profile for alot of the time if you don't want to be discovered by the towns authorities.
The game has alot to offer in terms of character actions: I have already mentioned powers of telekinisis, probing and laser guns but you can also change yourself into other forms disgusing yourself amoung others. And you can also brain wash people too. I suggest watching a trailer for the game so you can get a real feel for it (actions speak louder than words)
There are some down sides to the game, I found it did get boring in places and some of the missions seemed a bit pointless. Also it would have been nice to see how this game would have panned out if multiplayer were available. Also the game doesn't constitute of many characters making things seem almost lonely at times, wishing you had maybe a few more Aliens to help you in your task of world domination! Because lets face it one can't really do it alone.
All in all a very funny game Crypto's voice is spot on, and some of the cut scenes are very witty.