I played the unenhanced version 20 years ago or so and got as far as the Underdark, and remember feeling that there was still loads more to go.
In a recent playthough I got as far as Spellhold, thinking the same.
Now SoD exists, I've just started BG2EE after completing BG1EE and SoD, and I'm curious as to how much is actually left of the game.
Once I reach Spellhold, am I roughly 50% of the way through, or is it more than that?
I'm talking just BG2EE here, not TOB.
I'm quite a completionist, although if the main quest needs urgency I will tend to focus on that rather than side quests (such as the main quest in Mass Effect - it was literally called 'Race Against Time' so I just went at it rather than doing petty side quests for the UPS man).
The 'howlong' website lists it as 180 hours or so for a completionist playthrough. It only took me around 17 hours to get to Spellhold though, which suggests that there is loads of the game left after that.