I'm trying to remember the details from my homebrew system a few years ago ...
Most of the more powerful undead radiate cold. A deep bone chilling cold that no matter how many clothes you put on, you still feel cold. This was a good warning sign to the PCs ...
A few powerful undead radiate heat. They have eaten so much life that they are actually radiating life outwards. This would only generally occur after a massacre or similar feast.
On the other hand, vampires were living creatures. Related to humans, but lacking the ability to synthesize an important protein, they had to substitute by drinking the blood of humans (or similar). However, without this body chemistry they were quite a bit tougher and essentially did not age. Drinking blood was the only trait they had that was really typical of vampires. Yes, they suffered extreme sunburn, but they could live outside in the sun with appropriate cover. And garlic caused problems as well. But beyond that, none of this D&D vampires turning invisible, gaseous form, and so forth. Occasionally, vampires could have infertile offspring with humans (ala horse + donkey = mule), though most couplings would not result in a successful pregnancy. One of the PCs was a half vampire (a vampeal).
Culturally, vampires were the nobility on the continent where they dominated. There were rules about the size of their fiefdoms to ensure that a vampire has sufficiently many human peasants. Their (noble) job was to protect the peasants, in exchange for blood and taxes. Most of the vampires were fairly pleasant in this regard. Some were known for being cruel, overfeeding, and so forth.
In general, vampires were long lived and powerful. Their appetites were seen as a threat by other powers. As a result, the Covenant of Immortals (essentially powerful and ageless but otherwise mortals) specified that vampires were not allowed to become "immortal" and were to be prevented from achieving this. Now the Covenant of Immortals specified that the members ("immortals") agreed not to influence the mortal world (mostly passing through it and dealing only with immortal issues). The Covenant would mostly track down and kill immortals who broke the rules. I say "mostly" because certain immortals were intentionally left outside the Covenant so that they could ensure the vampires did not get powerful.
One immortal in particular, Julianna (if I recall the name correctly), had a small kingdom on part of the continent where the vampires mostly held sway. She and her followers would periodically go out and attempt to hunt down the most powerful vampires.
One of the most powerful vampires, close to immortality, was Deathwalker Rayburn. His eyes had been burned in a laser fight with Julianna. However, Deathwalker eventually developed basic seer abilities to see around him. (Seers generally blinded themselves at an early age to improve their foresight, though one race did not need to do so.) Deathwalker was reknowned for using a shotgun in battle, and disappearing when the going got tough, leaving a cloak behind on the ground as he vanished.
The party was eventually involved in an epic battle between Deathwalker Rayburn and Julianna. The esult of that was the opening of some seals releasing an ancient (20,000 years) vampire immortal. Then other immortals showed up to subdue that vampire, Julianna exited stage left with chagrin for having released the 9 seals to try and defeat Deathwalker. And the immortals finally allowed Deathwalker to join their ranks - the alternative being dealing with an increasingly powerful group of vampires who would have opposed the Covenant.