Here is an overview of the game, via The Pokemon Company:
In Pokemon Legends: Arceus, the Pokemon series takes a bold new direction, fusing action with RPG elements. The game takes place in the Sinnoh region of the past, long before the events of Pokemon Diamond Version and Pokemon Pearl Version. As the game’s protagonist, the player will set out to create and complete the region’s first Pokedex by catching, surveying, and researching the wild Pokemon that live there.
The cover art, revealed here for the first time, depicts Mount Coronet towering over the expanse of a bygone Sinnoh region—the setting for the story in Pokemon Legends: Arceus.
View a new artwork at the gallery.