So I really enjoyed Dawnguard-the story was great and the environments were fantastic. And they wrote a character they knew would strike a chord, namely, Serana (basically a vampire Cortana). Overall, she was well acted and had a few good lines of dialogue. Hey, it was sappy and cliche, but at least they tried to write in some family and personal conflicts this time, not just some rubbish about prophecy this and ancient that.
But all that aside one thing strikes me as stupid, Serana joining the Dawnguard and remaining a vampire.
It makes no sense. She only sided against her father because he was straight up evil. And she even harped on him for hurting 'innocent' vampires.
Now correct me if I'm wrong, but Serana has just barely won the acceptance, no, the tolerance of the Dawnguard because she vowed to kill Harkon. They don't want her around, they wanted to use her, and Isran was very clear about that.
And all that aside the Dawnguard ha vowed to kill all vampires, regardless of said vampire's agenda. So why would Serana join them? Or even stick around? To kill her own kind?
Now, if they had somehow written in that Serana gets cured it would be more believable but as it is I find it a bit much.
A better ending:
Serana takes over Volikhar and vows to begin a new order in her family's name that will not terrorize the innocent. She and Isran reach this understanding and vow not to interfere with each other's clans.
EDIT: I just read in the UESP she can be convinced to be cured....but my plot point still stands in general.