Having completed the game very recently, my thoughts about the endgame are:
Act 3 is easily the weakest part. Jumping right off the bat with the appearance of Orin and the murder quest felt a bit flat. I didn't spend enough time with any of the NPCs inside Baldur's Gate to care about whether or not saving them was important so I did everything else and Orin's appearances neither surprised me or shocked me at all.
It's the dead body of a random priest I don't remember the name of killed in some way. I didn't care. Oh hey it's a blacksmith, he starts asking questions about killing, okay Orin, you can shapeshift. Great. Literally the first two NPCs I talked to were Orin.
It's just too in your face.
Orin in my mind should have only made an appearance in Baldur's Gate once you've spent some time in there talking to people getting to know the city. You do a few quests and THEN it turns out you were talking to Orin at some point. You have no idea when. Was that guard who asked you to take care of a thug Orin the entire time?
Don't get me started on Gortash. People have already talked about his appearance so I won't go into that. His introduction was completely meh. The plot involving Gortash was underwhelming.
You have the option to ally with him to take down Orin, but I've already taken down Ketheric so at that point why do I care? He doesn't give you enough of a reason to ally with him to begin with, and he turns on you pretty much immediately if you want to save the Archduke as well. For a master of intrigue and manipulation to blatantly turn against you in your face was stupid. What he should have done was play nice until you got out and when you go to fight to Nether brain, if you rescued the Archduke despite his warning, he stabs you in the back so you have to fight him first. If you don't rescue the Archduke, and you allied with him, he helps you but you feel that he could turn on you at any moment and he never does? At least he should have a chance to betray you or based on some other factor, maybe a Steel Watcher sees you talking to a Deep Gnome and he sees it as a sign you're looking to undermine his authority, perhaps he knows you talked to his parents. He's not very subtle and if you're stupid enough to trust his pudgy little face and give him all three stones, then you deserve it. Otherwise he just dies in the cut scene if he's allied with you against the Netherbrain? Whoop-de-doo.
I'll probably think of more things that annoy me about the end game but this is what I have for the moment.
