What high profile game series is least in need of a design reboot? Probably Half-Life. Let's do it anyway. Mental exercise is good for you.
Tricky - Vent
Start back with "Ivan the Space Biker," the earliest incarnation of the Gordon Freeman character model. The chunky hazmat suit, the bushy beard, the flat-top hair cut, the Ted Kaczynski eyes; what's not to love?
We know Gordon Freeman as a cypher, a mute avatar that is nonetheless a heroic figure among videogame protagonists--but how different the original game would be if it were filtered through the perception of Ivan? What gameplay would match the his sensibility, the low constancy of his gutteral rantings?
Unlike the more winsome Dr. Freeman, let's assume Dr. Ivan is as deeply paranoid and reclusive as his appearance suggests.
You're clearly a long term employee of Black Mesa, knowing more than a few dark secrets but also intimately familiar with the layout of the place.
Your status as the facility's recluse means that your tenure at Black Mesa is tenuous at best (ha!)--so you're called to do some cart pushing in the test chamber. Reluctantly you agree in order to keep your job.
The catastropic events that follow might best be described as Diehard meets Andromeda Strain. And you say, "hold on, couldn't that trite movie pitch formula be used to describe the original Half-Life?" to which I say shut up, Dad. I learned it from you.
The game would play as a mayhem-filled survival horror scenario instead of heroic run and gun. As Dr. Ivan, you freak out and hole up in a pre-arranged safe room/storage area deep in depths of Black Mesa, emerging months later very hungry and with a prodigious beard growth, your worst fears confirmed.
Virtually all of your former colleagues are long dead. The US Military is still not far from using the nuclear option on the now alien-infested facility, though desperately trying to reclaim it with conventional means.
But as the time frame is far past that of the original game, the entire base is essentially "behind enemy lines." A First Person Stealth/Insanity Shooter (FPSIS). With cunning, ingenuity, and the self-preservation of a full-blown paranoiac, you'll guide Dr. Ivan to survival, escape... or is it that you've always secretly wanted to go to another dimension and never come back? And what's up with this Barney guy, anyway? Is he on the drugs?
On release, Dr. Ivan Just Can't Die receives a Metacritic rating of 73/100. The game develops a considerable cult following over some years (and a boost in sales once the v.01.05 patch is introduced, which allows players the option to turn off Ivan's rantings), but not enough to fund a sequel. Fans are left wondering just what a deranged, fascinating sequel might have followed from such a difficult, unusual game.