I must utterly disagree with the comment that PST used AD&D rules. It broke almost every rule to improve the game. Can't die. Stat gain each time you level. Change class at choice once you learn the basics of a class. Armour, no such thing. Alignment changes to match your actions. Several spells work differently to the standard rules. Non standard team NPCs that had many unique abilities. Able to modify your teams basic stats if you can work out how. Other than using The basic Strength, Agility, Constitution stats which most games use anyway it had nothing in common with other AD&D stuff.
Anyway NWN MP gamedesign put me off so I've never played it. Also since PST is a very different game I wouldn't group it either. I'd suggest
1) IceWind Dale 2 (I never played IWD1)
2) Divine Divinity
3) Diablo 2
4) Beyond Divinity
