Looks like they introduced attacking on Horseback, and crossbows, which they should've done a long time ago. Fortunately, modders have already beaten them to it. It seems somewhat interesting, this Dawnguard thing. Pretty much Vampires vs Slayers, with the option to choose a side. My guess is if you choose the Dawnguard you gain bonuses against vampires/undead etc... and if you choose vampires, you gain vampirism and the ability to transform.
I'm interested.