I think, I will talk about what drew me to Dark Sun in the first place when I was still new to the game. That is, if I can find the words.
First and foremost, it was so different from what I was used to. As much as I love knights and castles, I grew to love deserts and sorcerer-kings very quickly! A brutal world destroyed by magic, without gods, very little metal, and a pretty widespread disdain for the very force that shaped the planet. I'm pretty sure I read the player's guide in one sitting, I was so damn on board for this setting!
Second, the art. The beautiful cover art of Brom instantly drew me in, while the interior art of both Brom and Baxa kept me firmly entrenched in their amazing vision.
Third, the alien races. Half-Giants, Half-Dwarves (Muls), and, my favorite, the Thri-Kreen. Even the standard races were twisted along with the world they live in. Well, those that are still around anyway...RIP Gnomes.
Mind you, these are the things that got me into Dark Sun...I'm pretty terrible at selling things :-D