I've been a fan of the Ravenloft line for like 7 years now. I own the entire 3E line, as well as a considerable number of earlier products. I've always been intrigued by the setting, and I figure it would be a fun place to DM and play in. But, I've never DM'd a game in the Ravenloft setting.
You see, I feel that the whole "mood" would be lost on my group of players, as we have a typical jokey atmosphere, which would be hard if not impossible to curtail with some of these guys. They're pretty accustomed to being able to handle a lot, combat-wise; I don't really know how I would successfully instill any kind of fear in them.
The other thing is, I've been running the same 3E campaign since the new edition's debut in 2000. I really wouldn't want to make these guys start over with new characters, as the current party has a great dynamic, and I have some players who have a lot of problems settling into characters (character-of-the-week syndrome, sort of), though everyone has been happy with what they're playing for a while now. The highest level character in the group is 11th level (and the only character who's been there since I started the campaign 3 years ago), and the lowest is 8th.
So, um, any words of advice, Ravenloft fans?
I haven't actually gamed in a while, myself, so I may not be the most experienced person to tell you but some thoughts...
A "full mood atmosphere" type of DMing may not be completely possible with these guys (although I might still consider somethings), but remember you can still ensure that the characters get scared by using fear and horror checks. (They were put into the game for a reason, you know.) If your players are outraged by having to make these checks, then standard Ravenloft may not be for your group. (Of course, it has been noted that you can simply use the setting "as a backdrop for vampire bashing," but I wouldn't call that Ravenloft
I would recommend checking the Ravenloft Dungeon Master's Guide. It has many suggestions about different ways to play a Ravenloft game.
As for the question on party level question, to me the ideal way to play Ravenloft seems to be starting off from the outset (i.e. 1st level). However, average 10th level party could still function fine in Ravenloft. They just need tougher challenges, of course. (Don't forget to see Denizens of Darkness/Dread for monsters, of course).
First the atmosphere takes care of itself if you as DM do the leading. If you don't joke, take yourself and the material seriously then the PCs will follow (assuming they want a different experience, maybe they don't). Its hard to laugh things off when you as the DM continue to weave dark plotlines that touch on loss, corruption, betrayal, greed, wrath, vanity etc etc. Sure its still "chips and mountain dew" & funny the first time round...but gets less funny the more it goes on. Then its not funny.
As an aside when I first went to see the Two Towers everyone started laughing during the first Smeagol/Gollum dialouge...but the laughter died away by the time the time Gollum finished his list of crimes with a slow "Murderer". That's the way it was for me at the movie. Funny, then not so funny...
Second, a RL campaign really does deserve to be built from the ground up with first level PCs. Let the PCs know that there are plenty of "set" encounters in the world...if you march up to castle Ravenloft (or even the werewolf's cave) you get what is there...not necesarily what the DMG says is a Fair encounter for the PCs level. This doesn't mean that the PCs won't win most of their battles...but does mean they need to treat the setting with the kind of respect a skipper treats the ocean when out of sight of land.
-Eric Gorman