I had to think a while about the first game concept for a while, and I actually managed to come up with a loose formula that irons out the kinks (i.e., the "let bad guy kill you, body jack bad guy, ad infinitum"), as well as actually construct a loose story-line for a final product:
The setting is a near-future city (one with society slowly becoming more violent and unstable), with your character being one of several selectable archetypes: to put it in "Fighter, Mage, Thief" terms, the equivalents are "Soldier" (a former member of the army, who suffers from guilt at the things he did in the war), "Preacher" (a clergy member who fell out of their congregation, and often questions their faith in God), and "Runner" (a kid from the streets, who has resorted to petty crime to survive), although there are a lot more archetypes which blend elements of these three archetypes (more about them later). The Soldier has the highest health, and is skilled with heavy guns (assault rifles, shotguns, explosive launchers), and is a brutal close-quarters combatant, but is slow to move (since he has resorted to alcoholism and other substances to drown out his PTSD), and his melee is mostly limited to using the butt of his firearms as clubs, using a combat knife or machete, or just brawling with slow and klutzy punches, kicks, and grapples. The Runner is the fastest and agile, with free-running and parkour skills galore, while focusing on using light, concealable firearms(semi-auto pistols, light SMGs - anything that doesn't hinder his movement), and uses the widest range of melee weapons (preferring "swinging" blunt instruments, pocket knives, and brass knuckles), but is extremely fragile, and needs lots of finesse to successfully fight or take flight. The Preacher, although middling in terms of health and agility, has the lowest skills of any weapons - they make do with the power of their words to persuade human enemies out of fighting (and later, using magic and holy spells against the legions of Hell that can't be swayed by speeches).
The introduction shows an "average day" in the life of your selected archetype, with them having to put up with a situation that seems to happen to them - and countless others - every day in the city: fighting for survival. Each case is a tutorial in basic (i.e. pre-Vampirism) abilities: the Soldier gets in a bar brawl showcasing their up-close and personal melee combos, the Runner is forced to use their parkour to outrun a street gang and/or the police, and the Preacher has to talk down several assailants in a speech check. No archetype can get a "game over" if they don't complete their objective: their opponents just beat the crap out of them, and the only difference is that they get home more battered and bruised than if they had succeeded.
However, by the time the character gets back to whatever miserable wreck is their excuse for home, they end up being attacked in the night by a vampire. This first phase of this fight shows how to use defensive weapons/spells, with the Soldier and Runner hurriedly grabbing a melee weapon of choice to beat off what they believe to be a drug addict, while the Preacher falls back on a Lord's Prayer (or an equivalent of such) to ward off the evil creature. The second phase has the vampire suddenly start showing off his fancier moves (i.e. teleporting and clinging to the ceiling), the characters break out the offensive weapons/spells, with the Soldier and Runner drawing firearms, and the Preacher using incantations to damn the vampire. After a desperate fight, the character seemingly kills the vampire, who disintegrates into ash. Believing the fight to be over, the haggard protagonist collapses in relief, partly wondering why they were attacked, but mostly thankful to have "killed" whatever was attacking them.
However, the third phase of the fight has the spirit of the vampire rise from the ash, and try to hijack the protagonist. This starts a "Battle in the Center of the Mind", where the vampire distorts the protagonist's mind into relieving their darkest moments: the Soldier is brought back to the battle that their unit was killed at, the Runner relives the moments their family was slaughtered, the Priest is forced through the same event that got them exiled from the church. Then it becomes even more distorted and surreal as the vampire begins the battle in earnest, and the protagonist is barely able to defeat the beast. However, just before the vampire's soul is banished to oblivion, he tells the character that their battle was for naught: defeating him only made them recipients of the vampires curse, and they would be doomed to walk the earth until their soul is defeated, and will be damned forever in Hell.
Needless to say, the prospect of eternal damnation more than outweighs whatever longevity and superpowers the player gets now, and they thus become desperate to find some way to lift the curse from their shoulders. However, as they journey through the seedy underworld of the city, they will discover a plot be the vampire society to spread chaos in the city, allowing vampires to destroy the human population before moving across the world.
Anyways, the gimmick is that, instead of automatically possessing an enemy after death, one has to undergo a last-ditch attempt to possess the nearest enemy, and destroy their soul to get their new body (which is shown as a 1v1 duel with the person being possessed). If a player waits too long in trying to possess an enemy, their soul gets drained of energy, making the possession harder and more dangerous, and getting killed too many times in a row drains their soul of energy even faster. Boss enemies are of either other vampires, or particularly strong-willed humans, who are thus more harder to take down than standard enemies, but reap tons of XP, abilities, etc. when defeated. The end goal is to destroy the main vampire lord, whose death will break the character free from their bounds of vampirism, and put an end to the schemes of the vampire society against humanity.
So there you have it - a way to balance the mechanic of possessing enemies upon death, and a plot to get the player invested in the action.
Oh, and to fully explain the archtype system, there are three major skill trees a player can invest in: fight (which is raw damage resistance and firepower with conventional weaponry), flight (which focuses on agility and quick, lightweight weaponry), and faith (which relies on the powers of persuasion, and using holy items and weapons to repel enemies). The archetypes of Soldier, Runner and Priest are respectively fully invested in the fight, flight and faith trees. The following archtypes are either dominant in one tree while taking parts from the other trees, or evenly split between two trees:
* Gangster(Half Fight, Half Flight): A member of one of many street gangs in the city, this career criminal isn't quite as agile as the Runner, but has more experience with heavier weapons (such as sawn-off shotguns, or stockless assault rifles).
* Survivalist (Half Fight, Half Faith): A right-wing militia man, this archetype doesn't have as much firearms training as the Soldier or the religious teaching of the Preacher, but more than makes up for it by covering the areas the Soldier and the Preacher lack in.
* Goth (Half Flight, Half Faith): Although more of a hobbyist on the underworld than a true "child of the night", they are still able to come to grips with powers better than most, and are more agile than the Preacher.
* Police Officer (Half Fight, Quarter Flight, Quarter Faith): Mostly trained in cracking down on gangs, this archetype still has to rely on some running skills to catch fleeing suspects, and some ability to negotiate hostage situations.
* Con Artist (Half Flight, Quarter Fight, Quarter Faith): Mostly relying on a silver tongue (and a way to book it if a deal goes sour), this archetype is still able to use basic weapons if he finds himself caught in a corner.
* Private Investigator(Half Faith, Quarter Fight, Quarter Flight): The final archetype of the list, this Harry Dresden-esque PI has already had some dealings with the supernatural world, and reacts to his vampirism predicament with more irritation than panic.