As others have mentioned, Alienware is overpriced. If you're a gamer without much of a budget, you don't want to build your own PC, and you like your PC to have lots of lights, it's the way to go. Otherwise, choose another option. You can build your own, spec out a dell, etc. If you don't see the options you like you might also look into CyberPowerPC. I ordered a machine from them for someone and it seemed to go well and they provide lots of options at a reasonable price. Like Alienware they focus on the gamer market but you have a lot more options. It's much more like building your own PC but you don't have to fret so much over compatibility, how to install a motherboard, and you get a warranty. I built a ShuttleBox PC awhile back. Also a good experience but the small case sort of limits your options a bit and can get kindof warm if you're doing renderings or intensive CPU processing.
-Brodie