The base Area 51 model is $500 or so more expensive than what you could build yourself or find from a less expensive pre-built. The high end ALX model costs around $2,000 to $3,000 more than a self-built or comparable pre-built gaming PC with similar performance. A fancy case and pretty lighting are not enough to justify a couple thousand extra dollars.
The following two incidents are anecdotal, but if gaming media sites are to be believed, not unique.
1) I called in due to a boot up error warning of a non-functional fan. It sounded like the tech flipped through a manual to find reference to my problem, then started walking me through the support steps. I quickly realized what he was instructing me to do was change settings in the BIOS that would simply disable the warning. Fixing the actual problem was never part of the support call. Apparently, the goal was to get rid of the warning, let the malfunctioning fan continue to not do its job, and hope the heat never caused a meltdown of something important (at least not while under warranty). Who knows how many Alienware customers have lost important data to overheating simply because a fan failed and Alienware tech support instructed them to disable the warning.
2) Another time I called in to report a periodic, loud vibrating noise coming from inside the case. I had paid extra for sound dampening (a huge waste in my opinion - a well built PC with quality fans is pretty quiet), so this was particularly disturbing. Two hours on the phone failed to remedy the problem, so they made an appointment for an on site tech. The tech that arrived a few days later diagnosed the problem as a loose fan on the video card (Alienware has problems with fans it would seem), but the one he had with him didn't fit. They made a new appointment and ordered a fan part that would be mailed to me. At the second appointment, the tech opened the package that had arrived a few days prior and discovered the part they ordered did not fit. I was told to order a new part, and then replace it myself. He showed me where the fan would go and told me how to do it. That's it. That was some of the worst on-site tech support I have ever experienced.
I bought my first Alienware in the late 1990s and was a huge fan for almost a decade. Since then, quality and customization have slowly declined, while price has either stayed the same or gone up. Performance is still decent, so Alienware desktop PCs are not a complete waste of money. But there are many superior options for a PC with better performance, more options, better support, and/or less hassles.
In short: go elsewhere. If you want a pre-built, look at some of the less specialized, lower cost pre-built PC makers. If you are interested in building your own PC, do not be intimidated. It is not as hard as you might imagine. Picking out the parts you want is one of the hardest parts, and PC Gamer has a section in almost every issue (called "Hardware Trinity") that can help with that. Once you know what you want, cruise over to Newegg.com and select your parts. When they arrive, use this article - Building A PC - as a handy reference.