That is why we have so many bland but technically impressive games. Studios want safe bets, an FPS game is easy, making it interesting to play is still very hard.
Game engines and graphics is "solved" if you stick to popular concepts (which are those that are easily available in commercial engines).
Game design/mechanics is an unsolved problem imho - unless you consider it solved when merely taking an existing game design (like an FPS) and add nothing new to it (aka, those yearly COD military shooters).
Consider a game like https://store.steampowered.com/app/1141580/Taiji/ (inspired by the witness). This game is quite unique, and cannot really be recycled in to another game (without it being just a clone).
As they say: All good things must come to an end.
And: You either die a hero or live long enough to become a villain.