Let me add kindling to this bonfire, as a fan of both books and settings:
First, CoC d20 is wonderfully done, and has some feats and skills that should have been in DnD3e (Sleight of Hand and Skill Emphasis, for instance). That said, some players (and I'm speaking of experience) aren't too keen on the idea of playing session after session, adding levels to their characters, and all of this ammounts to nothing, since you can't ever be on par with most Mythos creatures (let alone the big octopus-face himself). I recommend CoC for short-term campaigns centered around a beatable villain (master cultist who, by the time the PCs get to 10th level, attempts to make the stars right).
Ravenloft 3e is a wonderful book. Those who complain about it are focusing only on the fact that it doesn't include the stats of the Darklords (which are in the DM-oriented Secrets of the Dread Realms). But here's a flash: you don't need them! You can play dozens of adventures without even once having your PCs meet any of the Darklords! And RL also has some of the best feats around, like the Ghostly Three: Ethereal Empathy, Haunted and Ghostsight. The 3e version infused the domains with more detail and personality than ever before. I sketched a map of the Core and highlighted the Cultural Levels of the domains. It makes perfect sense. It's like an 18th century Europe, with more and less advanced domains. So no Monster Island here (but how about letting a Tarrasque loose on Rokushima Tayoo?). In RL the PCs can level up and feel like they leveled up, it gives the players a sense of accomplishment. Eventually they can settle down in a bookstore or herbal shop and start publishing their memoirs. Or they can saddle up and ride all the way up to the castle and try (TRY, mind you) to take out the ultimate bad guy. And die.
Ravenloft -> Sleepy Hollow (for more advanced domains), 13th Warrior (for Early Medieval domains)
CoC -> In the Mouth of Madness (by John Carpenter), Re-Animator, The Thing.
That's all IMNSHO, of course!
