The only drawback of vampires in Heroes of Might and Magic V is their appearance, but in terms of characteristics: regeneration and retaliation are very good, making them decent in melee combat. If they had constant retaliation like griffins, they would be even better, but that's not necessary; their current level is sufficient. Besides, many players don't include them in their armies, which is a mistake. I always use them in battles, and neutral creatures don't attack them.