I'm really enjoying the new content in Ravenloft, but it also seems to be one of the buggier modules.
Some people have been reporting constant crashes, to the point where it made the game unplayable for them, which is fortunately something that hasn't affected me personally. However, I've seen plenty of bugs around the world.
While doing the rounds in Barovia I ran into two quests (out of five or six) that were so bugged that I had to drop them (though oddly, another time I managed to complete them successfully, so these particular bugs might not be entirely straightforward). Many of the new heroic encounters also seem to suffer from issues with spawn timers, so that you get situations such as being asked to "rescue hostages" but there are only a couple of mobs to kill and nobody to rescue... until ten minutes later, when the hostages suddenly spawn in.
It affects older zones as well: While doing the rounds in Omu with my pet tank last weekend, one of the patrol missions bugged out so badly that we were unable to complete it, as several of the mobs we were supposed to kill kept glitching into walls and refused to come out. (This one's supposed to be fixed by now according to the patch notes.)
However, the issue I currently find the most annoying is that when you're in Barovia, most of the time you can't see any of the other map instances except for one or two (while numbers indicate that actually there are more than thirty instances up). This makes it hard to casually hop around different maps to join groups for the big heroic encounter whenever it's up. Even going old school and asking for a group invite might not help, as I've gotten a nonsensical error message every time I tried to use the "transfer to their instance" prompt while grouped. Even leaving the map and coming back in only sometimes works to unite you with your group mates. It speaks for the quality of the module that people are playing enthusiastically despite of all these issues.