Perhaps a system that monitors each day that passes while a vampire, and everytwo ingame months you get alittle stronger, with damage for example. The system they've had for oblivion and skyrim for a vampire has be...well [censored] to be honest. Perhaps even the more you feed(restrict the amount of times you can feed everythree days for example) you get alittle stronger (but only alittle). It would build up in the end, after all they're ment to get stronger with age :toughninja:
I think the vampires feel a little tacked on, like they were put in as an afterthought or something. They should have claw attacks (like Khajiit) at the very least, and some quests would be nice. As for powers, well in the interests of balance you can't give them too much, but the vampiric drain power (I forget the actual name) only drains 4 health per second at it's strongest. This is pretty pathetic for a low - mid level character and laughable at the higher levels.
I love vampires and vampire lore, I've read Montague Summers and watched most decent vampire flicks. Got into the White Wolf RPG Vampire: The Masquerade as a kid and played it on PC.
But for all that I prefer werewolves in this game, they feel more complete and powerful.