I've had no personal experience in buying an alienware computer although from what i've seen looking on their site and from their monthly newsletter alienware computers are very good when it comes to performance and are specially made for gamers. I'd however suggest going for one of the top end ones though.
They're expensive, but they perform and look damn good I've always wanted one, and one day I will definatly get one, but they're just too expensive for me at the moment. Besides, nothing can beat making your own PC
Yeah, and by them recommending another company you get your answer.
In my eyes Alienware's are good computers, just a bit overpriced when you really look at the guts inside and what it would cost to build it yourself or to have a similar machine made at your local computer shop.