We've danced this dance a thousand times before, but once more for the road: just look at these games. Baldur's Gate Complete. Baldur's Gate II Complete Edition. Icewind Dale Complete Edition. Icewind Dale II Complete Edition. Planescape Torment. (And The Temple Of Elemental Evil, more's the pity).
Now buy them. Even GOG can't match GamersGate's big fat bundle.