I can tell you what was wrong with Baldur's Gate: it was simply TOO big. I suspect it's why BG2 got cut down in size a lot compared to BG1. While it was great to explore the vast outdoor areas of the Sword Coast, there were too many areas with not a lot really going on that you just wandered through killing stuff. In terms of actual substantive content, the number of outdoor areas could easily have been halved without losing anything.
DD got the balance right: the sense of scale enough to make it seem like a real world, without there being too much of it.
Not that I didn't love BG. I'm just not blind to its flaws
