What makes Alienware (gaming laptops in general) Laptops special?

Most of the Alienware laptops have upgradeable components so future games can be run without a problem. Most laptops have the sound and graphic cards integrated into the motherboard. These can't be upgraded other than possibly a CPU and extra RAM. The Alienware laptop graphic and audio cards can be upgraded if need be. They are expensive, but if you need to "trade up" to a different laptop every 1 or 2 years, that gets expensive too.

The answer to your question is:

mostly nothing. Similarly specced machines perform similarly. Alienware is simply marketing to people who want a "gaming" laptop, but a professional 3d modeling laptop might have the same specs. Also, alienware puts cool lights and speakers in their laptops.
msi should be fine, as previously stated, but what really ends up mattering is durability and battery life. Think about it, nothing works if it physically can't handle you traveling. And nothing works if the battery is dead. Of course you want a nice gpu in it, but honestly, you are going to be browsing and facebooking etc, for far more allotted time. And an extremely powerful cpu and gpu will require big fans, making it heavy, making the battery die. Aim for the least power you can live with, while still running the games you like, a huge battery, and sturdy construction. I find asus, dell, and apple to fit this profile the best. Apple is expensive, it's true, but they use crazy strong materials, and excellent internal components, and usually have a lightly powered but capable gpu. Dell is also renowned for building tanky stuff, and asus to a lesser degree, but with a better warranty, respectively.

a haswell core i3 with integrated graphics will run any game but the absolute newest on medium settings, and will do so for hours on end. I once played starcraft 2 on an i3, quite playably, in an airport for 4 hours. An i7 with a 780m will run any game in the world on high settings… For about 45 minutes… With your legs on fire.