BG2 is still one of my favorite games of all time, although the recent surge of superb CRPGs and my newfound obsession with Dark Souls and Hollow Knight have pushed it down a few notches. It sat at the top for a very, very long time - specifically because, as some other posters have commented, it's just such a huge game with so much going on. A long time ago, when Westwood Studios still existed, I played RTS games almost exclusively; BG2 was my first big RPG and having a decent amount of RTS blood in it helped me get into the genre. (Funny enough though, when I played BG1 years later, I wasn't too impressed by it).
That all being said, though, I still think PoE1 is a better game overall than BG2, because the mechanics are so much better. PoE2 isn't there quite yet, but it has a ton of potential. Don't forget how much better PoE1 is now than it was at launch. (To be fair, I haven't yet completed a 100% playthrough because I was waiting for PotD buffs and now I'm a little too busy to devote myself to another run, so there's still time for Deadfire to already be great).