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 😀.