They are great gaming notebooks and can serve as a desktop replacement system with ease. Drawbacks include being quite heavy/bulky so carrying them around can be a pain and battery life isn't all that great. You have to admit, though, that they look really cool as well.
For the most part, most places will say that the Alienware M17x is the top of the line for gaming laptops. but come with a hefty price tag.
But there are so many other gaming laptops out there, pay a little extra to get the 1920x1080 display and such and it's sitting at somewhere around 1900 USD.
But then there are the Asus G53 series notebooks with similar specs at around 1400 USD. As well as MSI notebooks and the Toshiba Qosimo's. I've never seen any of these machines tested head to head however, so I have no clue which would be better.
Except for Toshiba, I've owned a laptop from each of these companies.. all have about the same quality when it comes to service and support. So I guess it would come down to how much you are willing to spend, how much you want to customize your laptop.. and if the color changing led's are for you.
Im hearing more and more that the gaming laptops have had increasingly more problems with heat, drivers, etc.
Im not sure to what extent this is true, but if you look up a certain model in newegg and read feedbacks, you might get a general idea on how good ppl think a laptop is.