Color me old-fashioned here, but I liked how in Oblivion, if you did not feed for long enough, the sun began to damage you, which made it REALLY realistic because you HAD to avoid the sun and stay in the shadows, the way a vampire should be. Now, in Skyrim, the sun does not hurt you, but only impairs your stats and stunts regeneration. That is cool as well, but I prefer how in Oblivion, no feeding = damage by sun. Which in my opinion, seems more realistic, as far as vampirism goes.
I don't really care whether I'm a vampire or not; I do like how it doesn't make your character look ridiculously stupid like it tended to in Oblivion, and how you get lots of useful skills as well. It has a lot of benefits to it, for sure.
However, I dislike how in Skyrim, you can be cured in a snap of your fingers. WHAT? Is it really THAT easy to shake off the vampiric blessing of a Daedra lord? In Oblivion, you practically had to go through hell and high water to be cured, and that was a once-only kind of cure! In Skyrim, it's like, "Oh, you're a vampire? Go get me a stone and boom, you're done." And you can get cured as many times as you want. That just doesn't seem right... I prefer the Oblivion version of getting cured. It felt way more important, way more well-earned.
Sorry for ranting :3