Let's see - BG 1 opens with you fleeing Candlekeep only to watch your Adoptive father insta-killed by a powerful big bad, who is clearly after you. Shortly thereafter you start running into Assassins', harpers and even Elminster.
BG 2 opens with you, your sister, and your comrades in arms captured, tortured and killed, an escape from a dungeon of nasties followed immediately by a passel of powerful mages arresting your sister.
Both suggested some fairly high level adventures in your future - though it might takes many hours of play to get there.
While BG 3 does open with Mindflayers, Demons and Dragons they are all busy fighting with each other - they have little to no interest in you, only the most tangential of involvement with you at that point, and your eventual "escape" is circumstantial at best - you have little control over the outcome of the situation. From then on, any high level content is mostly hints, omens, harbingers and future possibilities. Nothing screaming immediate, impending epic-ness is upon you.
The only real difference between the openings in BG 1/2 and BG 3 is technology has allowed for much more involved cut-scenes, rather than just a picture or two and narration to describe what brought you to this adventure.
