For a movie as bad as this one, I think it's best to start with what I liked.
As others have pointed out, this movie has a decent start. After Barnabas' backstory, it introduces Victoria in the Collins house. She was likeable, the set looked good, and although the exposition was forced, I was actually interested.
It looks great. The Collins' house is beautiful, the 70's looked cool, and so on.
Oddly enough, I kind of liked the villain most out of all the characters. Eva Green is having a ball with Angelique, and is a very entertaining Bitch in Sheep's Clothing.
That aside, this film has many, many problems, ones which I can't believe no one making this film noticed.
Most of the other characters were simply underwritten, especially David and his father. They could have been cut without affecting much of the story.
Next, the romance between Barnabas and Victoria. It's weak. As I said, Victoria shows up at the start, but then disappears throughout most of the movie, except for a few scenes just before the climax. It's almost insulting that they expected me to believe that they love each other when they have no chemistry, no real development, and hardly any scenes with just the two of them.
Next, there's Barnabas. While Depp is great, as usual, this is hardly his best work. He's funny at first, but never tries to blend in, and it gets stale quickly. The character himself I didn't like either, simply because he's a murderer. He kills about twenty people, never shows any sort of shock, horror, shame, etc. Even worse, the movie expects me to forget them, going from him slaughtering people to fish-out-of-water jokes. Why should I like him? How is he better than Angelique? Why should I root for a callous murderer? I've seen other murderers before that I kind of like, but he isn't likeable enough, and the people he kills aren't despicable enough for me to root for him. Although I haven't seen the show, I hear that Barnabas was a villain there who tried to overcome his bloodlust, and that this doesn't do him justice.
Lastly, there's a pointless twist at the end which comes out of nowhere, and adds absolutely nothing to the story. That's all I will say on that.
Overall, a bit of ironing out would have made this a much better movie. It's clear they had too much story and not enough time.