I am conflicted. On the one hand, I do not think it is a good setting at all. The domains are single-dimensional. Like Megaman bosses. Frankenstein man. Dracula man. Etc. There is little mystery to uncover and minimal scope for players to affect the setting. There is a kind of metaphysical restraint.
I suppose a campaign could end with “beating” Ravenloft, with each domain as something like a level with a boss (thinking again in video game terms). I did not see that at all when I first encountered the setting in the 90s and I do not think it is really present in the actual materials (though admittedly I have not read them in a while). It is something that the referee and players would need to bring themselves (and could just as easily be brought to any other setting). The Hammer Horror cliches are a nice variation from traditional fantasy cliches, but are cliches nonetheless (and can easily result in similar saturation).
On the other hand, the mists are an atmospheric mechanical constraint and explanation. They provide a reason for the relatively static nature of the place and also serve as a form of magical-realist logic that can give the setting a dreamlike sense of archetypal reality (much like the mythic underworld or the setting of Dark Souls) if handled well. That is, the distinctive part of Ravenloft seems to be a good justification for having multiple, target rich environments. I am not sure that such justification is really all that necessary for a satisfying game though.
This reflection was prompted by Jeff R.’s recent posts on what makes a good setting.