Among all the starting classes in Lunacid vampires are by far the most unique option. Here's a quick list of unique mechanics from my fresh melee vampire playthrough.

Helpful quirks:

• Attacking most enemies in melee starts very slow health regen that's interrupted by taking any damage. The same effect is also caused by having "water" status in the Sanguine Sea or when interacting with blood fountains in the Castle Le Fanu.
• Blood Wine restores both health and mana. The item is fairly rare though, I only got 3 during the entire game.
• Most doors in the Castle Le Fanu will be open without vampiric symbols.

Problematic quirks:

• Recovery from bleeding and blood magic is really, REALLY slow. It basically makes blood magic very annoying to use.
• Having "water" status in other locations deal constant damage, making the rat area in the sewers really dangerous.
• Holy water deals a lot of damage when used. It still removes statuses though!

Honestly, I didn't really like how vampires are played - they felt like a challenge class actually. Their advantages are questionable while their disadvantages are disastrous. Also, their heal on melee attacks doesn't stack with the blade of Ophelia which is a shame because I was relying on it for the second half of the game.