User blog comment:Nerakil/Did you prefer the Dawnguard faction or Volkihar clan?/@comment-3492791-20121212044854/@comment-5046408-20121218161739

The upgrades come through sidequests for the female Breton Dawnguard you recruit (Sorene, I think?). But yeah, crossbows pretty much made Skyrim much more entertaining than it was before, mainly because it's the closest thing to a gun you can get to in TES, and it makes the game feel more FPS-like in combat. I still use that weapon as my preferred means of ranged damage, especially with the exploding bolts >=)