If you put it in your deck, it's worth getting
Historic is a format with an abundance of ramp cards such as Growth Spiral, Explore, Uro, and much more, so getting six mana into play quickly is a strong possibility
While the life loss and gain synergy provides incremental advantage, there are better cards with similar effects, such as Zulaport Cutthroat or Blood Artist, which have lower mana costs and provide more immediate impact
There is no auction house or way to sell cards
Marneus is certainly powerful, but some say the card is a lazy design and that the deck builds itself
Indulgent Aristocrat The cards that spread +1/+1 counters to all your Vampires are the main way to turn your simple tokens into massive threats