In my experience it's like 2 players have full agency to play independently, unlike other coop games where the experience for player two is often driven by player one.

In BG3 you can run off in completely different directions, engage with your own NPCs in conversation while the other player starts a fight and it's seamless

I've played both divinity games in co-op with my partner. You have an entire (quasi) open world game fully explorable by both players independently. At one point in the main town in DOS1, I was running around tracking clues for a mystery while my partner (a rogue) was stealing everything she could get her hands on from the market. Once I reached the climax of the mystery quest, we joined back up for the final battle.

This freedom engenders a lot of creative flexibility and is just overall a chill way to play a game together. I agree that it makes for the best co-op experience I've ever played (especially when you're playing with an otherwise non-gamer).

And for that reason I've also pre-ordered BG3 😀.