Haven't finished BG/BG2 yet, I had to reformat but I'm reinstalling tonight. So far they're my favorites of the bunch.
I need to reinstall Planescape: Terment after re-buying it from GOG because I have a disc version with a game ending bug. Worse yet, it was sold to me without the manual or packaging in a "D&D Bundle!" at Fred Myers some nine years ago along with Soulbringer. What I played of PT is great, though.
IWD2 is AD&D 3.+ ed, so I never bought it or played it, so I can't list it.
Never played IWD 2.
The only reason why I put BG1 over BG2 is because of the first time I entered the screen leading to Buldur's Gate, the music and plot actually made me feel I was in a story.
I put Torment last because the story was not engaging.. BUT Morte was the best character in the series.
I haven't thought of a second run through the BG series, but you guys have me interested again.
--- BUT ---
If your main character gets eliminated during the game, accept it. Start another game. Don't save your game during your session. When you want to end your session, go into Options, select Quit, select Save.
I'm telling you, playing the game that way is far more challenging strategically and tactically.
If you want my justifications for these things, I can provide them. If not? I'll say it right now: Icewind Dale 2 doesn't implement 3rd edition rules all that well and has some seriously off-kilter pacing.
At the time of its release, I was deeply immersed into 3 console game systems (Playstation 2, XBOX & Gamecube) for several years before returning to the PC.
On topic, I have a hard time comparing BG, IWD and PST as it's like comparing apples, oranges and bananas.
IWD is great because you can fully customize all your characters and the story doesn't get in the way of the action. Dialog is at a minimum (See next paragraph why that's a good thing) and it's over quickly so you can get back into the action and tackle those orcs holed up behind a trapped bridge. Problem with IWD is later on the game, it gets too easy and when the game starts getting too easy, you just want to finish it quick. There's also the issue of getting swarmed when you enter an area, but hey, just leave, rest, go back in, bash some more, rinse and repeat. I don't really like that kinda cheese in my games.
BG is great as you have a good balance between action and story, lots of places to visit and explore in any order you like. Problem is BG games is the dialog writing is terrible. Dialog wise, your only choices are a do gooder response or a stupid evil response killing any chance at roleplaying your character's decisions which for me, kills some of the immersion. If you don't choose the "good" responses in dialog, you miss out on XP and loot essentially forcing you to play a good character. I just finished playing through BG1 and some of my dialog options made me cringe. Still, I picked the "good" one cos that's where the loot and XP are *sigh*.
PST is good as it's a through provoking adventure touching on morality and philosophy and the action doesn't get in the way of the story. Dialog is well done, story telling is well paced for the most part and the setting is just great, I love love to see another game in the PS universe. Bad thing about PST is low replayability. Once you've played through with a high wisdom and intelligence scores, you've pretty much seen everything the game has to offer.
In the end, it's all what you're looking for. Is it a well told story, non-stop action or somewhere in between?