NWN2, especially if you're an old PNP vet from the old days of rolling the dice, play acting every sentient creature in front of others, and getting excited when you roll "double damage - instant death"!
Make sure you upgrade to the latest patch, which corrects some notorious bugs. The player community is starting to create persistent worlds right now, but there's a collection of modules that are ready for you to download and play after the original campaign ("OC").
If the original NWN1 is any indication, this will be around for a while, with plenty of AI tweaks, mods, modules, and other misc stuff to come - courtesy of the gaming community.
You're limited to 4 NPCs in the first third of the OC, and 3 in the remainder of the campaign, but this can be overwritten through "DebugMode 1" - then you can add up to six NPCs for nice melee screenshots.
The D&D rules are so in-depth (v3.5), and cover all sorts of physics - magic included.
I used to think I was a hardcore D&Der, but after reading a few threads at the Bioware site, I'm just an average schmuck D&Der!