Why I like Ravenloft
1) Ravenloft is the only way I can play Dungeons and Dragons. I'm not a high fantasy guy. I don't care all that much about elves and dwarves. Give me vampires staring out over lonely battlements any day.
2) Ravenloft takes place in a fantasy world called the Domain of Dread, dominated by every trope of gothic horror you can imagine. Frankenstein's monster roams the countryside looking for his creator. Werewolves prowl the forests. Ghosts creep through ruined castles. The few heroes who attempt to fight against the darkness must act with great care, lest the corruption consume their own souls.
3) The world of Ravenloft is ruled by the Dark Powers, a mysterious consciousness that often takes the form of the mists that constantly shrouds the Domain of Dread. We never get a clear sense of what the Dark Powers are, but they seem to be focused on subjecting the inhabitants of the domain to moral tests and punishing those who fail.
4) Ravenloft is built around grand gothic tragedy. The doomed warlords of tiny fiefdoms in the realm--darklords, in the game's parlance--are trapped to forever reenact the dramas that lead to their downfalls. The tyrant's armies will always fail in conquest, the mad wizard will never be able to learn any new magic, the vampire will always find and lose the reincarnation of his first love.
5) Unlike most of Dungeons and Dragons, Ravenloft heavily emphasizes the story. Most of the powers that Dungeons and Dragons players rely on are corrupted by the Dark Powers. Gods are inaccessible, scrying and divination spells don't work the way they're supposed to, and traditional routes to power often come at horrible cost.
6) Because the Doman of Dread acts as a moral test of character, and because the Dark Powers seem to favor evil (or at least attempt to put the forces of good through the toughest gauntlet imaginable), the players' actions often draw them down the path of corruption. Hiding behind alignment no longer works, as selfish or evil actions can condemn a character just as thoroughly as any darklord.
7) The Domain of Dread works for pretty much any kind of gothic horror adventure, from Van Helsing's lethal crusade to quieter works of spirits in lonely manors. The emphasis on atmosphere and narrative versatility make Ravenloft one of my favorite creations in all horror fiction.
Conclusion: I like to think of Ravenloft as the land where all horror stories come from. Almost every classic monster is represented in one form or another, tied into a cohesive whole. It hits the right mix of tragedy and dread that makes for great gaming and storytelling.