Acadian: There are no vampires in fallout. They do have ghouls, but they are not supernatural creatures, just people mutated by radiation who look like zombies. Some are feral, and attack everyone they see. Some are 'normal', and just look different. They do have extremely long life spans, perhaps immortality (save for catching bullets of course).
I just play Blood Raven as a normal character with glowing red eyes. My only change to the rules is that she cannot use Stimpacks for healing like everyone else. Instead I modded the blood packs in the game to provide the same healing benefits. I also took some traits from a trait mod I use to help simulate vampirism, such as regeneration. It has lots of other traits you can pick to customize your character beyond the normal perks you can learn as you level up. Most of my characters take one or two. For example, Hecate always has the Four Eyes trait, which gives you a bonus to Perception when you wear glasses, and penalty if you do not.
The big guy is a Super Mutant Behemoth. Super Mutants are like ghouls, in that they are both mutants, and they apparently do not die of old age. Instead Super Mutants get larger and larger the older the become. The oldest ones are like these Behemoths, gigantic. They are one of the biggest boss enemies in the game.
In the end, there can be only oneHard hat areaArmored upIron giantsMichael Bay momentGhoul disarmamentThe TES V power armorBetween light and darkness