They added characters. I think they did it to give Abraham more reason to fight for slavery than just to fight the vampires. Will Johnson was not in the original story, but I think he replaced Jack Armstrong from the book very well, though their stories are very different. Will is a free black man who gets involved in the Underground Railroad, where Jack is the leader of a gang in a city Abraham lived as a young man. They both help Abraham in the same way, though.
Adam, the vampire in the movie, was not in the book either, but I suppose they needed a definite enemy to fight. The book was more about fighting the uprising vampires as a whole. With most scenes in the movie played out between the good Abraham and bad Adam, I suppose it only makes sense that those scenes don’t appear in the book. Still, I was greatly disappointed that they removed most, if not all, of the historical accuracy of the book. I found that was what brought the whole story its charm.
One thing I did like about the characters was Abraham Lincoln, himself. Benjamin Walker did an excellent job portraying Lincoln. He had the height and gangly nature, along with the strength and grace needed to portray the Vampire Hunter side as well. Makeup and costuming were excellent too.
I understand that Seth Grahame-Smith wrote the screenplay (he was the book’s author), but I was really surprised that none of the original story was really in there. There were a lot of gory scenes in the movie, but it was on par with other movies like Blade or Underworld. I personally felt like a lot of the plot was rushed so that you could basically get to the fight scenes that were CGI beauties. Right in the middle of the movie, there is a watercolor montage scene that was gorgeous but felt out of place from the rest of the film. Character development wasn’t there as much either, and reading the book doesn’t really help because, well, the characters and stories are much different in the book.
If you want to see beautiful, yet gory, CGI fights painted on the canvas of a very strange, and more inaccurate than not, portrayal of our history, then this movie is for you. But my honest opinion? Read the book, skip the movie.