I beat the Dawnguard side of the DLC in roughly six hours. That's was playing it from as soon as I got it non stop. I admit I ran through a certain heavily infested area", but yeah I ended it pretty quickly. Not really a bad thing though.

So did anyone else beat a storyline?

I beat both sides and every quest (besides the unending sidequests)

Like, two weeks ago

6 hours? I spent 30 playing Dawnguard before I beat it. You must have really rushed through it. I wonder how much you missed.