Firstly, I am absolutely flabbergasted by the negative reviews for Siege of Dragonspear. It really seems like Beamdog were stuck in a no-win scenario: if they change anything, they ruin the spirit of Baldur's gate; if they change nothing, there are too few improvements. I put playing this on hold for many years due to the negative criticism, and I can now after completing it definitely say that it is totally unreserved. Note that I played this in 2021, so bugs which may have affected early players may be gone now. I think the story is decent (not great, but surely not terrible) and gives an interesting account of the events occurring between BG1 and BG2. I didn't expect much in this regard, so I was happy to see that. I also felt that both the quests, dialog and environments were very much in the spirit of Baldur's Gate. The main difference is the linearity of the story and chapters. However, I expected an expansion pack, not a new game, and as such I am without a doubt satisfied with this and had a really good time. And just a comment on the "political content": there is absolutely nothing in this game that is more out of place than anything in either BG1 or BG2.
