I can explain the bad reviews:
Baldur's gate 2 is probably the best CRPG of all time (my personal favourite) and the fans have all loved it for 20 years. Comparing Siege of Dragonspear to BG2 (an incomparable masterpiece) is just stupid. Nothing will match BG2 in terms of story-telling and immersion.
BUT if you've played BG/Icewind dale and love the style, the gameplay, the visual aesthetic, its all here. They mixed up the combat and items and created a game experience that doesn't try to be the original, but still let me relive some of its glory.
After about 4-5 hours into the expansion, I'm having tons of fun with it. It's been almost a decade since I beat the original saga, and it feels good to be back.
I'm actually surprised by all the reviews. As far as my experience goes, I haven't encountered any bugs so far, the party banter is brilliant, Corwin is an interesting character, and the dialogs are well written.
Combat in DnD-based games was never my forte, so I like the new difficulty options. I also like the increased stack size for ammo and other items.
I might revisit this review once I finish the expansion, but so far I like it a lot.
I just played this for the first time, and the bugs that seemed to have been prevalent upon first release are mostly gone as of Spring 2017. The game crashed for me twice (both time while loading a cut-scene), but the auto save retained the content-- meaning there was no loss of progress and no problems other than momentary irritation.
Some of the criticisms of the game seem fair: it is more linear than either of the two main games; there are sections with trivial runaround quests; and I understand why the ending (after the completion of the main quest) could seem like an anti-climax to some (it serves as transition material between the first and second games).
That said, it is still the best expansion in the series (and, yes, that includes Throne of Bhaal), and it was fun to re-visit the Baldur's Gate world. I started from the original Baldur's Gate and worked my way up to the expansion, and I will probably go ahead and take the same character through Throne of Bhaal for old time's sake. I would recommend you do the same (at least the starting from the beginning part), as the experience will be much more satisfying. If you also remember that this is an expansion-- and not a sequel, you are more likely to come away impressed, rather than be disappointed.
I would also suggest recruiting the Goblin shaman M'Khiin. She is by far the most interesting new character, and she is more powerful than she first appears (eventually filling a valuable niche in the party).
As to some of the other complaints (there is a transgender character, and you don't have the option to be nasty to her; the female characters have more agency than in the original games; and there is the possibility of homosexual romance): the less said about these, the better. Some people can only feel big by trying to make others feel small.
Overall: if you're a fan of the original games, it's worth your time (though not essential)
This excellent expansion was clearly made in the spirit of Baldur's gate 2. The characters and the plot are great (the storytelling has really advanced from BG:EE). If there were many bugs in the original version, they must have been largely fixed, because I haven't seen them (playing this in 2018).
I love the goblin shaman NPC!
First, I'd say this game is just fun. For the most part, it feels like a genuine sequel, even if you don't have the same freedom to move about in the world in this game as in the last.
One problem I have with this expansion/sequel is its length. It's far shorter than Baldur's Gate: Enhanced Edition. For that reason, I'm unsure why there is no difference in price between the two. There's also the issue that if any of your characters are permanently killed in the first game (blown apart, burnt to a crisp, etc.), they might return in this game. That kind of feels like a cheat, but it's not a big deal. I'm also a bit puzzled and annoyed by what Beamdog does with Imoen in this game.