Ah, I was pretty much a NWN 2 defender here on these boards, but I've come to the conclusion that it was mostly because I powered through the beginning and lingered in act 2, where most of the openness is. I thought the trial and the keep were awesome.
But then my computer crashed and I needed to replay to get back to those awesome parts. Not fun. Not not not not fun.
So to answer your questions, the OC is 30 to 60 hours long, depending upon how obsessive you are. I ended upon the 60 hour end, because I will cart my items between merchants, writing down prices and going back & forth until I get the best deals. And I'll read and reread the dialogues. And I pause like crazy and micromanage my companions in battle. All of that combines to make the game looooooonnng. And it made act 1 unbearable when I went back to it.
The real problem is the railroading. I didn't notice my first time through because of the faux dialogue choices. I honestly believed that companions could be refused -- there is the dialogue choice that implies you're not open to taking on a companion, so I assumed you could opt to not take on a companion. But then I actually tried some of those and realized they simply force you to the same decision, like it or not.
On second play through, you realize how many of the areas are railroaded, too. You have to do almost all of them, every time, in the same order. This was fine my first time through, but again miserable the second time through (and flat-out unbearable the third -- I just gave up and put away the game).
The middle of the game is better. There are some real choices, not fake. But it also kills me that my favorite alignment (chaotic good) is shafted here. You have to choose between becoming the proponent of lawfulness, or engaging in evil. A lawful evil character would have a hey-day, because both choices could work for him. But chaotic good? Totally forced to act out of character for looong stretches.
As for whether there are boxed off areas as in NWN 1, yeah, I'd say that's pretty much unchanged. Well, there is a prettier interface for it all. But you'll still wait for locations to load, and click on exit points and all of that.
The engine itself is pretty great. I'd suggest that you buy it, play a few minutes of the OC just to get some background feel for the story (at least, until you're aggravated) and then download Purgatorio or whatever gamer-made modules are out & highly-rated. Getting a character to level 18 is pretty easy with just a couple fan-made modules. Then put that character into MotB.