I gave a try and made my Sim a vampire, I found that It is very fun! Buuuuuuuuuuuut the major problem are to feed, plasma packs, plasma fruits and plasma salad fruit don't feed you very well and you have to reapeat those foods all the time, this is a letdown if youre already used to play with a Sim, with max Cooking and the "no hunger" perk.
While you can feed of other Sims, it's totally not immersive, as they and the bystanders really don't care if there are a vampire nearby sucking the blood of the others, It should be more sneaky, I don't see the point of vampire form because It really doesn't matters.
What I wish to see in this pack for It to shine: more dishes for vampires, your vampire secret identity should matters, Sims disliking and afraid of you if they know that youre a vampire, have some kind of spell to make a Sim your troll.