It should be lore friendly.
Sun damage
Increases in Strength, Speed and Agility
Blood dependancy
Increase in power/ability with age
More in tune with the lore(more mystical and magical)
More feral appearance(and able to conceal appearance with hoods/helmets)
More ways to feed i.e. sneak, quick kill, feed on fallen enemy
Chance to infect
Faction Bloodlines and quests
I'm sure there can be more than this.