PC version you console players might be lucky but the DG DLC is full of bugs how i manage to complete the game was I had to reinstall Skyrim then start from a fresh new character disable all mods and then manage to complete Dawnguard though it was still a slog uphill.

Some of the bugs i came across before I started with new character. Playing with my main lvl 48

Sarena disappears when meeting up with her mother and mum and daughter talk with each other. She faded right in front or me, can't carry on because the dialogue needs to be completed before the next trigger.

While doing a dungeon quest for the DG side i ran through the stairs which took me outside of the map character stuck

Fell through the floor while fighting a gargoyle ending outside of the map

Could not complete the vampire side because keyboard would go dead so couldn't carry on the quest where i was asked to use my vamp powers.

getting the blood elder scroll was impossible because when i would go to pick it up the dialogue that should have triggered afterwards never triggered.

Collecting the moths after collecting them i am suppose to read the scroll but nothing happens the scroll is read but doesn't trigger to the next part. Stuck.

Many of them i had to enter the Setstage codes to bypass the bugs and carry on but this only made me miss stuff and it got to the point where i was googling for the next code to bypass the next bug.

Fresh character, mods disabled, reinstall of Skyrim. Leveled him up to 15 and started the DG quest only came across one bug with the DG side, but still couldn't complete the vampire side because of the keyboard lock.

IMO and from the forums ive read plenty of players have the same bugs/glitches its not worth buying until a patch is out or when the DLC price is $1.99 or near abouts. 

Bethsheda messed this one up totally.