Great Detective Pikachu was just released in the Japanese 3DS eShop. You can view the game’s introduction above.
No release date has been announced for any other country yet. This is possibly because of all the casting (*coughdannydevitocough*) and dubbing that will be required. It appears to be heavily story and character-driven.
It looks like Pikachu learned all its detective skills from its Trainer, who then died in a car accident. This game shows the Pokemon world in a way we’ve never seen it in a game before – it looks like a lot of effort went into it. They should totally make this into an anime one day!