In comparison to the original Baldur's Gate, Icewind Dale wins hands down IMHO (I dislike the first Baldur's Gate alot). But compared to Baldur's Gate 2, well......it's a tough choice. Meaning, I can't decide since both have their ups and downs when compared to each other.
Icewind Dale Pros:
-Can create all of your party members by scratch and make them any way you want.
-The game ends when *all* party members die (as opposed to the game being over if your primary character dies).
-No shoehorned romance to deal with, annoying party members, and bickerings.
-Fights are more varied and interesting.
-Many fights are challenging and keep you on your toes.
-Has alot of fights and action.
-Interesting locations and settings.
-Mages are better IMHO since they have more offensive spells.
-Lacks cheap mage fights.
-Jeremy Soul's excellent music (though there isn't much).
Icewind Dale Cons:
-Thin story since it focuses on action (but that's a given for this series)
-Lacks interesting boss fights.
-No dialogue option to let you know that your weapons are ineffective against certain monsters.
-Not as much music as Baldur's Gate 2.
-Fairly short compared to Baldur's Gate 2.
-No Kits (I'm spoiled with the kits in Baldur's Gate 2).
-No Experience points for reading spells or disaring traps (anyone know of a Mod that fixes this?).
-The expansion is rather dull and uninteresting.
-No special abilities for high level characters.
Baldur's Gate 2 Pros:
-A good story (though there are bits I morally disagree with and it can get too Black & White at times).
-Great boss fights such as Dragons & Demogorgon himself!
-Has a good expansion (though I favor Watcher's Keep the most).
-Kits for variety.
-Experience points for disarming traps and reading spells.
-The Underdark! My criticism for Baldur's Gate 2 is that it lacks variety of enemies and lacks challenging fights (outside of bosses and super cheap mags). But this is not the case with the Underdark, as it has a great variety of challenging enemies and it's a great settng. The first time I went to the Underdark, it felt like I was in Hell! Even Diablo 2's hell levels didn't creep me out as much as the Underdark! Kudos to Bioware fo doing a great job with this area!
-Special abilities for high level characters.
Baldur's Gate 2 Cons:
-Shoehorned romances.
-Annoying party members.
-The only party member you can create is your primary character.
-And if your primary character dies, it's instantly "Game Over" Very annoying at times!
-Very cheap feeling mage fights.
-Lack of offensive mage spells.
-The vast majority of fights are boring (except for the Underdark and it's denizens), though this is remedied in the later parts of baldur's Gate 2 and Throne of Bhaal.
PsychoWedge: You forgot the music. It's one of Soule's finest works. xD
I really liked the story in IWD2. It's rather subtle and by no means in the front or the driving force but it is one of these stories that Black Isle seems to have favoured so much. You know, where it's not so much about pure evil and pure good and saving kingdom and country but moves more on these personal levels of human behaviour. IWD2 was one of the very few games were I was angry as the end unfolded and wanted to join the villains to march against the good guys.
I sort of felt the same way. I was really angry with the Ten Towns since I partly blamed them for what happened with Issair and Madae. And if there is one thin that really annoys me is how Faerun treats half races. But I also really liked how they made the story not as black & white (take the hint, Bioware!). But at the end of Icewind Dale 2, I recall didn't feel all that heroic when I understood that had Issair and Madae been treated better (and Half races for that matter), maybe none of the events of Icewind Dale 2 would never have happened. I felt like leaving the Icewind Dale region and never coming back again.