Black Isle was closed by Interplay.
NWN was made by Bioware, and is a really good game, but itwas never or intended to be BG3. I should check and see how many disks the Platinum edition is, its a pain installing everything seperately.
KOTOR 1 is good, KOTOR 2 was pretty lackluster. Corners were cut, bugs, choppy story, underdeveloped characters, etc. Stick with one.
Bioware is currently making a 'spiritual successor' to Baldur's Gate, under the name Dragon Age, which should be really good.
In the mean time, if you want good story in a SP RPG, you're pretty much left with NWN and its thousands of user created modules.