While I am trying to avoid significant spoilers for the game, Avowed seems to be more combat-heavy and less flexible in terms of the story (e.g. all companions are mandatory). I would hope Avowed to be closer to immersive sims, considering the first-person camera perspective, with their detailed level design and multiple ways to resolve quests, and Pillars of Eternity II, which supported the player's agency in terms of narrative and consistently high-quality writing, but I am unsure at the moment how it is going to be. In terms of sustainability, the lower system requirements, the better (<20GB storage space, <4GB VRAM would be ideal), which is even less likely to happen.
Still, it is an Obsidian game and I am looking forward to it. I also hope to be able to purchase it on GOG on release (highly unlikely) to prevent any updates that can significantly worsen my experience.