In my experience, the former Black Isle guys can write tighter code/script/dialogs than the Bioware guys can.
And Bioware's been slipping. For example, NWN's scripts and dialogs felt like a step backward from
BG2's, which I suppose happens sometimes when you're doing a major engine rewrite.
BG2 had the advantage of being built upon
BG1's framework, so more time could be spent on the finer points. It took them until HotU to finally do a consistently decent job on the details that matter. I do enjoy that campaign.
The only thing I didn't care for in BI's
IWD series were the way some maps felt like "Oh, empty space, lets fill it as much as possible with a pointless maze of rooms." I much preferred
BG2's (generally) sensible area layout.
Still, I plan on buying a copy of NWN2 as soon as it hits local stores. That way I can play it and use the toolset, and then submit bugs before the patch cycle inevitably ends. After all, NWN is up to version 1.67 now (I finally got a copy of it when it was at 1.66) and I'm constantly finding bugs/issues that Bioware never bothered to address. They have mentioned another patch will be released, though it will mostly contain new content for mod-writers. Regardless, I just sent them a list of bugs I found. Hopefully it got through the filters.