Just beat Vampire arc of [Skyrim] Dawnguard. Considering playing Dawnguard arc with my other character.
Less fun than the Shivering Isles expansion, but isn't bad. The follower you get in the vampire arc is pretty good.
Being a Vampire Lord ... It's more powerful than being a werewolf, but has the same limit of not being able to access the inventory or your shouts etc., and you also can't interact with anything other than levers or doors, so I feel like there's little point. You can level it up, but so many people are required to absorb (note: you can't just bite sleeping NPCs to level, you have to absorb them AS a Vamp Lord), it feels pointless to even morph. I'm playing on Master as a level 40-something, so very few things are easy enough to absorb as a Vamp Lord without being able to heal with spells or potions, so I can't level it.
So basically it just forced my character to have immunity to poison & such, have cool glowing eyes, a nifty/cost-less Night Eye, but ... Little other benefit. Weighed against being VERY weak to fire damage, universally hated after 5 days without drinking blood, and lacking the ability to regen HP, MP, or Fatigue while out in the sun. (Lame.)
Maybe someone'll mod it to actually being useful.