D&D is the most well known, and entry level game out there. That's why so many play it.
Back in the day I picked up a World of Darkness book, and in the 'example of play' section, it was all about playing out a romance between the PCs and the DM or some such. I decided to go back to elves and spells.
Anyways, if your players just went hack and slashing through Ravenloft and Darksun, I think there was something missing. Darksun is supposed to be incredibly brutal, with death around the corner at all times from an uncaring world, and Ravenloft is like the undead version of that, where the world really is out to get you.
My campaign is all homemade stuff, cities, overworld maps, dungeons, etc. One thing I tell my players early on is that not everything is beatable. Just because they encounter it, doesn't mean it can be overcome, and you have to decide what to go after and what you can really do. After a warrior idiotically charged a dozen peaceful myconids, and died for it, they got the idea pretty well that fuckups will kill them. Since then, they've been quite cautious, and we've actually had entire sessions without any real fighting or hack and slash, just talking to various NPCs, dealing with issues, exploring the cities, rooting out mysteries, etc etc. It's been 3 sessions since they've seen a dungeon actually.
Really, it's not about the system so much, as about how you run it.