No,no,no all of them are very different games.

Icewind dale 1 & 2:
RPGs using D&D system for monster killing fun.

Baldur's Gate 1 & 2:
....Seriously does the epic rise of Bhaalspawn need be explained or justified.

Planescape: Torment:
The game for RPG stories to be compared to. The antithesis of Icewind Dale series really.

Even though Icewind Dale, Baldur's Gate, and Planescape use the same engine, ruleset, and are in the same genre, they are very different games.

Baldur's Gate 1 and 2 are a make your party over time sort of game.

Icewind Dale 1 is make your party at the start sort of game on the same engine and premises of BG1 and 2.

Icewind Dale 2 is that same engine except using 3rd edition D&D rules.

Planescape: Torment is massively dialogue and story heavy on the infinity engine.

I'd maybe sub out ID2 for Might and Magic 1-6.

i just made the purchase, thank you guys very much. have any awesome moments to share? lol

Just go in sequence.

BG1 then 2, go to Heroes 3 to mix things up. Then using the info you've gleamed in BG1 and 2 make your party in ID1.

And definitely read the manuals GOG provides. 2nd edition D&D is pretty complex.

There is no game quite like Planescape.

I'd say that all those games are worth buying though.

I should put this in a text file so I can handily copy/paste but with BG1 and 2 make sure you use either the 'tutu' or 'BG trilogy' community patches to play BG1 with the BG2 engine - its much improved!