Larian needs to understand that in D:OS a party size of 4 could work fine given that D:OS is a classless system. But D&D is a class-based system, and the different classes are a foundational core characteristic of D&D. If you go with only a party of 4, you might as well not bother creating all of the many more esoteric classes available in D&D because nobody is going to be able to use them anyway. Like many have already said, you basically always need a fighter, a rogue, a cleric, and an arcane caster. No space in your party for any ecclectic characters. No space in your party for that character who is dead-weight in combat but so much fun to have for roleplaying purposes. In a D&D game, that's a terrible shame.
It worked well in NWN2. It's not about how many party members you have but game balance. I liked playing BG with 4 or 5 party members personally rather than 6.
