When I played BG1/BG2 back when they released, both came off as goofy to me. There was a lots of joke characters, jokes played on NPCs, funny situations, pop culture references and sarcastic one liners ever two dialog selections. Most evil characters were just too over the top or melodramatic to be taken seriously too. The graphics didn't look particularity menacing or dark to me either.
What I've seen of BG3 so far is some adventuring in daylight and inside a very dark ruin with some gloomy night time chat about having a parasite eating your brain that will eventually turn everyone into mind flayers. It also included bloodsucking a party member... Looks plenty dark toned to me.
