^ I had the same question actually; the vampire lore in the movie seems slightly fuzzy in a couple places, and how people get turned is one of them. Of course, I have been watching Buffy lately, so more used to that being spelled out.
Also, as pointed out, it seems odd that at one point Henry couldn't touch Adam, but at the end they could beat on each other no problem. Maybe Adam was just lying and had Henry in some sort of thrall the first time? Afterall, Henry also had no problem throwing around Coats on the docks. Actually, it could be as simple as vampries can't kill
other vampires but can wail on each other no problem - hence the silver knife Henry couldn't use.
However, despite these minor quibbles I thought it was very good overall. Ben Walker did a great job as Abe and I agree with the "young Liam Neeson" remarks. Would've liked to see more Mary Elizabeth Winstead, but that may just be me and she was good in what she got.
io9 is definitely full of shit, and despite the inherent silliness of the concept and the constant slam-bang action through the first half (the fighting-in-a-herd-of-horses was great) I really really like the story. I mean, if you're going to turn antebellum slaveholders into mythological monsters, vampires is pretty much a perfect fit. Pampered elite sustained on the blood of innocents clinging to old ways maintaining a crafted "romantic" air and holding masses in thrall? Yup.
I thought that it was obvious that Joshua Speed didn't betray Lincoln but in fact was a part of the plan to lure all of the vampires onto the train?
It was revealed a bit too quickly I think. I definitely caught it and thought it was a really awesome moment - especially with lying to Henry as well - but it might have flashed by a bit.