This was a very well researched book, I was half expecting to be reading it and inwardly dying at the unrealistic vampire stuff, but... Seth Grahame-Smith described the events in such a realistic way, I was almost half-believing it.
However the ending (Abe's assassination) was a little dragged out. I could see what Seth was trying to do; give perspective from other characters and a lot of foreshadowing, but it only made the pace slower. I was expecting the end to be one mass murder of vampires (since I think the blurb told me they grew extinct after Abe), but apparently there were still plenty wandering around. I may be mistaken though.
Another part I had a problem with is the two dreams that Abe has. Seth uses the same method of pretending the dream actually happens, then Abe "waking up". The first time was fine, but the second was pretty much a repetition and that shouldn't happen too often in a novel.
This was a well written novel, the characters were well developed. I only wish I knew more about Henry, since he proved so interesting, but very little was actually known about him. The most insightful part was when he was caring for Abe after the vampire-boat incident, and that seemed to be completely different from the Henry that writes the letters.