Jarmo: Agreed, OC doesn't deserve it's poor rep. It does repeat a lot of the same story elements bioware always repeats, but why single it out?
I would say because it is worst at the start, which is when most people will be making their judgments on it. Running around Neverwinter opening crates seemingly left everywhere with 3-4 gold each inside was not one of my happier memories. It does have good parts (Charnwood Village notably) and the NPCs did have a reasonable amount of story behind them but overall the best description one could give of the OC is "patchy" in my view.
The party member limitations (one henchman only and no inventory control) didn't help either - although things were improved in the expansions and NWN2, they're still some way from the Infinity Engine's 6 character party (I guess Bioware found it easier to cover up their rotten pathfinding by limiting party size rather than fixing it properly).
Graphics-wise, I'd agree with you - the IE engines had some breathtaking scenery that nothing in NWN (or NWN2) can hold a candle to. NWN particularly suffers with outdoor scenery ("plastic trees").
In fairness though, Bioware were going through a bad period (in legal dispute with their publisher Interplay) and the
original plan for the NWN campaign was far more ambitious. Maybe someone will try making it one day...