Yes, get the Diamond edition.
It gives you access to:
- NWN Vanilla
- Xpac 1: Shadows of Undrentide
- Xpac 2: Hordes of the Underdark
- Extra Module: Kingmaker
- Extra Module: Shadowguard
- Extra Module: Witch's Wake
Each of the above have their own campaigns. NWN Vanilla and Xpac1, you should start with brand new characters. Xpac2 is the sequel to Xpac1, so you can import you Xpac1 character after you finish that. The 'extra modules' will level you up to the needed level, so you should start those with new characters too.
Depending on how much you like combat/hack&slash, you might or might not be recommended by other people to avoid NWN Vanilla, since that one is particularly combat-heavy. The others might or might not feature a lot of combat too, but some might attest to their having better stories. It is all, of course, in the eye of the beholder.