If you take this movie so serious you'll be disappointed 'cause it's not. But if you take it as fun movie, fulled of action/fantasy/horror scenes and as what it is then you can give it a chance. Maybe, the character of Abraham Lincoln defined as vampire slayer is naive and childish and is not what you expected to see for historical important figure. Maybe someone thinks that this is disgrace for the character. And finally maybe someone thinks there is a storyline abstraction 'cause the book is better and I don't doubt that even I haven't read it. All this defects are not so important if you like movies in this kind of genre like Underworld, Resident Evil etc. This was a movie that deserves attention and give it a try.
Review of Abraham Lincoln: Vampire Hunter
