When I say modifications, that means scouring the forums for blogs, posts and notes (I view all modules as coloring books, meant to be filled in the way I think would best fit my game).
As Hawk Diesel says, Strahd is probably the weakest part, as written. As written, he is a jerk who taunts low-level PCs for no real reason and pops in from time to time to throw a fireball and run away. It makes absolutely no sense for anyone who has taken time to read the novels (e.g. "I, Strahd") or has run a villain. I would never run him like this, ever. In my game, he is obsessed with recreating events from the past to bring Tatyana to him. Nothing else matters to him. He may appear callous with regards to life, but he's well aware he's in a carbon copy of reality, and he can treat these shades however he sees fit. He's convinced he's right, he's convinced he's going to succeed eventually, and he needs things to go differently this time. The PCs become a means to an end once he realizes Ireena is attached to them. They can push her, convince her, make it turn out differently than all the other times he's lost her. And why shouldn't they? Eventually, he'll invite them to dinner and make it clear he's going to succeed, in this lifetime or another. He'll just wait for her to be reborn and try again, so why fight it? Why not convince her to give in, go to him willingly, and leave Barovia?
Despair wins. Once the party has given up, the Land becomes stronger, and it doesn't let go once it has tasted that despair. So yeah, when you fill in the blanks, make Strahd more like his novel character, the 5E version can get pretty epic.