5 out of 5 rating for Curse of Strahd
Mystery? check.
Creepy weirdness? check.
Sandboxy? check.
Entertaining NPCs? check.
Megadungeon? check.
Powerful boss monster who messes with the PCs constantly? check.
I've never been a particular Ravenloft fan, but this adventure manages to hit all the right notes for me. The location-based organization works extremely well, even in a campaign where NPCs have a bit of agency independent from the players. Chris Perkins' writing is fantastic -- colorful and evocative, yet clear when it needs to be. All of the monsters and magic item stats are well-done, the balance or technical concerns that I sometimes see in modules where a third-party has done a lot of the development work.
My complaints about the module are minor. In a few places, the read-aloud text is too long, sometimes as long as half a page! Generally, my players zone out after 2-3 sentences, max. Also, while the isometric maps of the castle are beautiful, they are not very useful as battle maps for VTT or for printing/projecting on a table.
Ravenloft isn't quite the typical generic-fantasy setting, but it isn't too far off, either; and yet it manages to feel very different. The pervasive horror elements and bleak tone really make Barovia feel like a different sort of place. A place I want my players to be very, very engaged with.