Really, I've found that the only downside of Vamp is the opportunity cost of not having another skill set available - which is not inconsiderable - but it provides benefits as is, and is not really all that weakened by loss of food and regen. There are many, MANY ways of healing in this game. Too many. Even on GRPD, I've never once needed to have them all active at once. Eating corpses is as good as any regen/food in-between-battles heal-over-time option. And during melee, you gain back health (and later, mana) for engaging in something you were already doing for free: namely, duking it out hand-to-hand. It gives you the melee benefits from both Necro and Blood Mage in a single skill tree. This only synergizes well with a Gish build - one that's got plenty of magic power while dealing out melee damage - and perhaps needs Perception or Alchemy to back it up - but in that context it works pretty well. To be competitive with other skills, it could use some more buffs and a new capstone, but the basic mechanics are sound enough.