How is the gameplay in the new Baldur's Gate expansion? Is it well balanced? Is it fair?

Or is the expansion a horrible pile of unbalanced mess?

(For purposes of this topic, I am only asking about the gameplay, not about the plot or dialogue.)

It is a pile of unbalanced mess that makes combat completely tedious with constant beasts respawns, not difficult mind you, tedious since most of the time they are trash mobs thrown at you, there is also a difficulty bug that if you play on Legacy of Bhaal turns it back to Storymode and doesn't let you change it, and multiplayer, is still broken.

Then there is the UI which is horrible but Beamdog has promised to fix it, let's see.

The story and writting are cringy, you encounter a character who constantly refers to you with "ohh maaan heeeyy maaan" and I won't get into the "social commentary".

It's not BG1 style gameplay. It's like Icewind Dale grind fest. I will just add that I played as a cleric, and one of the very many bugs is that Turn Undead just does not work... at all.

I like the game-play, but unlike most people, I enjoyed the added content in the original Enhanced Editions. I do think SoD is better quality than the new content in the original EEs.

One thing I've been curious about: obviously BG1 has a level cap, and BG2 starts you out at that same amount of experience -- presumably this means you go through all of SoD at the exact same level? Is that as boring and unpleasant as it sounds?

No, the level cap in BG1 was about level 8 for most characters, here you can get to level 10 easily with most classes. But yeah, it is still boring and unpleasant. It also makes BG2 even more of a breeze.