Pokemon Legends: Arceus is a lot like a traditional Pokemon game, with a focus on capturing, training, and battling a wide selection of pocket monsters. But it's also very unlike a mainline Pokemon game, with a more action-oriented approach, the ability to capture Pokemon without battling, and a distinct focus on wide open spaces. Those distinctions make a big difference in how long you can expect Legends: Arceus to last compared to standard Pokemon RPG, and how the story structure plays out in general.
But of course, there's lots to do in the post-game. Continuing your save after completing the main story will present you with an entirely new story mission to pursue, as well as the larger meta-goal of filling out the Pokedex and achieving the rest of your star rankings.
Once a new area opens, the story missions mostly revolve around getting in touch with a Noble Pokemon's Warden, learning what kinds of Balms it requires, and using it to soothe the wild beast in a boss battle. During the process of these story missions, you'll also gain access to a new mount, which will often open up new exploration opportunities. Upon finishing a boss battle, your captain will tell you the next star ranking you need to achieve to unlock the next area, if you haven't already reached it.
By the time you've soothed all five Noble Pokemon, you'll have completed all five star rankings necessary for the main story. That will begin the end-game sequence, which we won't spoil here.
For more on Pokemon Legends: Arceus, check out our beginner's tips, and how to raise your star ranking quickly. Plus, be sure to read our Pokemon Legends: Arceus review.