I've been through the NWN OC twice as well. Once when it was released and once a coupla years back.
I have to admit, I still remember being bored by it's progress and finding some parts of it to be somewhat uninspiring at release. The ineptitude and general lack of companions was also a big shock coming so fast off of the IE games. The plot was also pretty bizzaro and barely worth following. But that was about as far as my criticism went. They just happen to be quite big criticisms that can't help but shape someone's enjoyment of the game.
However, there was enough there to keep me until the end and there were plenty of memorable encounters, such as the dual Dragons, the boss in the sewers, stalking around wealthy homes. And it didn't feel particularly linear which was nice, it actually felt like a gigantic city, which is actually quite rare in RPGs and one of the points where they did IMO improve on BG2 even. I can't begin to list all the RPGs where the primary settlement consists of so few dwellings you'd think the Orcs would have raised it on a drunken Sunday afternoon imbetween a barbecue and going fishing.
The second time I played it some of the criticisms had reduced because, firstly, it's a lot quicker knowing where you're going, so the sense of boredom doesn't get a chance to linger so long in boring areas. Secondly, I knew not to care about the plot and just treat it like adventure for the sake of adventure, like a sort of aRPG with cRPG elements.
3/3.5 is also quite a fun D&D system regardless of everything else.
I agree it's held up well to the test of time with regards to looks and user-friendliness. I believe it still sells quite well and doesn't have graphics whores turning their nose up at it to any great extent like they might refuse to play IE and earlier games for looks-alone reasons.
But the main beauty of NWN still has to be the expansions and modding community. In this regard there are no words to adequately say just how poor the OC was in comparison to the extra stuff it produced. Which is a shame, because most people will play the series chronologically and I suspect a sizeable audience is lost during the somewhat bloated OC.