Vampires should physically change from not feeding. Why is it that at stage 4 everyone knows that I am a vampire? I look exactly the same. The vampire's facial features should morph into a almost demonic looking face. Think vampires from Buffy, like this http://i115.photobucket.com/albums/n301/captmorgan72/angel-vampire-face.jpg Then make them immortal, just like the immortal npcs in the game. You can be beaten down but not killed, unless fire is used on you. Then you will die. Just those two changes would make vampires much more interesting to play as.
Much of the [unrelated to TES] vampire fiction implies that the older they get the more powerfull they get, and that their appearance is largely under their control; (when they
are in control).
It might be cool to have a mod that makes all vampires essential, and weapons or events (that can kill vampires) clear that essential flag. PCs could (theoretically) get up again after death... like after a fall, or after slain on the road by bandits. Knowledgable opponents could finish them off if they know them to be a vampire ~just as the PC could for vampire opponents.
Werewolves should also be immortal and should never die from any weapon that isn't silver.
That surprises me... Yes I agree that for the 2½ minutes, they should only be harmed by silver... but would also rather the curse have a mind of its own, and not be a morph on demand player option. (Or is it on demand? I don't have Skyrim yet.)