GAME 1:
Make Anachronox-like (Aliens and humans goofing around) open world game + Cyberpunk environment + Deus Ex RPG mechanics + Vampire The Masquerade Bloodlines dialogues; where you discover "alternate reality travelling device", Then something gets broken and parts of the city you're in start having ripples allowing different environments to create chaos: Cthulhian Mythos creatures start in the Harbor sector, Zombies/Undead in Commercial Areas, Despotic (from several time periods) Soldiers in various iconic places (museums+plazas+governments areas), Vampires and Werewolf warfare amidst the sewers, Derelict neighborhoods and High Class Clubs, Industrial area modified by Legendary Creatures and Organized Crime trying to regain some, Steampunk Pirate Vessels clashing in the sky against futuristic flying vehicles.
A buttload of Guns + Melee weapons + Augmentations/powers: (Mechanical / Nano / Transformations)
Chapter 1: lots of Civilians running around, fleeing, surviving at the first chapters; Then resistance pocket groups + army support are being organized in spared zones and bases of the Big city + rural area + underwater scenery;
Chapter 2: you choose between which factions you support or on the contrary get their situation in a worse state Depending on what you want to do to get the ""alternate reality travelling device" back to it's functionality by getting to specific parts or organs.
Chapter 3: Then Psychotic Mastermind + Lunatic Artificial Minion, appear among the rabble of a Mental Institution, consequence of the collapse, allying several foes and creating a new regime under their rule. Random scenes of Civilians being Transformed, Embraced, Whacked, Recruited or eaten.
Chapter 4: rebuild places (different possibilities), gain allies (you choose whom), Travel to other locations (outer space smaller or bigger maps) Then return either as Spy/Resistance Leader, Bloodthirsty Conqueror, Diplomat, or Join the enemy against former allies.
-End of Game 1-
Game 2
(sequels are never better):
Starts with you, years after, as a dude who got a job in that famously reconstructed Mental Institute helping your Nemesis for his Therapy, and finding some mystery about who or what led you to the previous discovery of the "Alternate Reality Travelling Device" ARTD.
OR, about you getting up the Hierarchy of the installed Regime, through Political Intrigue, spy network, assassination, etc, until you discover something else through your information networks about the ARTD aka the "Alternate Reality Travelling Device" !