Gods & Monsters is being made by the same team that did Assassin's Creed Odyssey, but it certainly doesn't look like that game. Wondering why a more whimsical approach was taken? Creative Director Jonathan Dumont explained in an interview with Gamefreak365.
The style and the art direction that we gave for Gods and Monsters is inspired by a desire for us to make a much lighter experience for our players, something more inviting. When we started researching it, the Ghibli Studio vibe that they had for their movies was very interesting for us. Of course, it doesn’t translate one to one for games – and we have our own spin on it – but that was a very interesting manner to treat something fairly realistic but with more of a shaded version of it. And then we wanted to have that painterly feeling to have a little bit more of that texture like aquarelle into what we’re doing. So it gives it a unique feeling for our game.