Skyrim with dinosaurs.
You are a caveman in a prehistoric world of classical dinosaurs, think giant lizards, not birds. You explore vast, steaming jungles and craggy desert canyons with deadly tar pits all centered around a giant volcano which is the end game area where you fight a giant serpent god that lives inside it, in order to prevent an eruption that will destroy everything around it.
Found your own tribes and build your own camps for them, bang lusty, scantily clad cave women (the game will be politically incorrect) to help the human race propagate and hunt not only dinosaurs, but in some areas vicious saber tooth tigers and Wooly Mammoths, as well as go up against less evolved neanderthals in their vast, creepy cave complexes.
The game will have a campy vibe and art style that evokes the classic idea of prehistoric life from 1950s/1960s b movies.
Bonus DLC adventure can be you getting sucked through a time portal to a future dusty southwestern desert town that is also now overrun with dinosaurs.
In my mind's eye I can see this game so clearly, I wish I could get it made.
Alternatively Skyrim in mythical old Japan, you are a samurai hunting down Oni, Tengu, Kappas and so on, in your off time you can spend your quest money banging lusty geishas (more political incorrectness), stuff like that, lol.
20,000 Leagues Under The Sea: The Game: pilot the Nautilus through a vast, open world undersea environment, discover and explore locations like the graveyard of lost ships or the Lost City of Atlantis, but watch out for giant squids!
Ace Combat in WW1: a spinoff of the Ace Combat series dealing with Strangereal's equivalent to WW1 which according to series lore occurred sometime in the 1900s, it could continue the series trademark blend of real life military hardware and speculative technology, but this time with a steampunk bent.
We just really in general need a WW1 dog fighting game done with modern tech.
Fatal Frame Goes West: a spinoff of the Fatal Frame series where instead of Japan, the setting is in either a US or English haunted mansion, but you still use the Camera Obscura to bust ghosts (I'm actually surprised Tecmo never thought to do this with the series)