Its funny everybody seems to have forgotten Icewind Dale...it came out after BG1. Different developper, same engine, riding off on the success of a great game. It was an EXACT visual copy of BG, no one complained at the time, why now?
Im aware you cant please everyone, but my guess is there are way more people that like the D:OS style than people that dont. And I personally believe that using it for BG3 is a good move.
The number of people who like or dislike the D:OS look is irrelevant. The only thing that matters is whether liking/disliking the D:OS look is a deal-breaker for a person. BG3 and D:OS2 are supposedly two completely unrelated games. So one looking like the other is not even something one could or should expect. As such, if BG3 did NOT look like D:OS2, that's not going to alienate a D:OS2 fan. OTOH, for someone who disliked the look of D:OS2, it IS a turnoff to have this game have the same art-style look of a game they disliked. So Larian absolutely loses out by mimicking the D:OS2 look. And Swen and other Larian folks themselves have acknowledged as much by saying, in interviews back in February, that they are concerned about the criticism that this game looks too much like a D:OS game.
As for your BG-IwD comparison, it is apples to oranges. BG and IwD are BOTH D&D games and are BOTH using the exact same setting. For all intents and purposes, one (IwD) is a spinoff of the other. So those two games sharing a common "look" is to be expected and perfectly reasonable. There are absolutely no such connections between D:OS2 and BG3.
