Ideas dump. You may or may not get sued if you steal one of those...
Genre: Survival horror/Puzzle solving
First person perspective
Based on the pseudosceintific theory that memories can be stored not only in brain, but also in all individual cells of one's body.
The story is simple - someone dies and several people receive organ transplants from that person's body. You are one of them. A long while after you're out of hospital, your health gets much worse. Further examination reveals that state of all your organs gets worse - except for the transplanted one, which grows stronger. In some time you receive visions from organ donor's life, and strange paranormal occurences happen all around you. You find out that other patients after transplantations are in the same situation. You must find a way to get out of this shit, and (not necessarily) help others.
TLDR: Organ donor is a douche and returns as a ghost to kill you and get it's organs back!
Evil vs Evil scenario. Deep in enormous caverns under some accursed desert lie ruins of a great ancient civilisation. After ages of lying dormant you awaken - one of the Death Lords that brought aforementioned civ to it's ruins. Your goal - breach to the surface. But to do this, you'll have to get an undead army, and you're in a wonderful place to get it, as that place is an enormous, ancient graveyard! But alongside you, other death lords awaken and each and every one of them wants to rule both undeground and topside world. War of the undead starts!
Player would have unlimited power, but would be limited by resources - bones needed to animate undead. Excavating them from ruind and graves would be necessary. There'll be several starting units which would split into varieties based on one stat, like mobility, offense, defense. There'll be also neutral or outright enemy units - like ghouls that'd attack both you and your enemies.
Genre: Strategy/Survival/Hack and slash
Humanity turned away from gods after plague outbreaks and great war - gods turn away from humanity and open gates of Underworld, letting countless undead and other monstrosities like demons or dark spirits into the world.
In singleplayer campaign, player would control a group of undead hunters that have to clear off some area, survive, find out what caused the cataclysm and stop it.
In multiplayer, player would control only one character in given scenario and would have to cooperate with others to complete objectives or survive.
Edit: Forgot to mention this one
Nocturne: Black Heart of Jeramesh
Genre: Survival horror/puzzle solving
Third Person Perspective Shooter
Remember the old game Nocturne made by Terminal Reality, where you played as an agent of secret government organisation fighting monsters and paranormal? It ended with a horrible case of a cliffhanger... But this idea is not to continue story after that point. It's rather like one of chapter's of the game - seemingly unconnected story, just another case. This time, Stranger would be sent to investigate mysterious abductions and paranormal phenomena in the city of Jeramesh.