Think early castlevania and you got the most general concept of it.
Basicly the entire setting is set in a pocket dimension (thats how they explain it now to fit into most worlds). It has a village of scared townsfolk, lots of forests with a variety of creatures (gypsies, fae, werewolves, wolves, vampires, undead, etc), and a castle in the distance that is home to count strahd (a master vampire). In the last book (return to castle ravenloft), strahd had different goals determined at the start of the campaign and how he roleplays (hes either a gentleman or insane), therewere common elements. Such as a special order that fought undead but is almost extinct (was a prestige class people could earn), key magic items, strahds infatuation with a woman he belives is the reincarnation of his lost love. Its actually an interesting setting. You could wiki Dnd ravenloft for more info.