Having just beaten the game, here's my quick take.
Everything gameplay related in NWN2 is awful. The camera is awful and makes exploring a drag, a feeling furthered by the frequent loading delays. NPCs and enemies are idiotic, and controlling your party is a huge pain in the ass. Characters lag behind, rush ahead, and generally do whatever they can to screw things up. There's too much loot, and without a lot of knowledge of AD&D rules it can be difficult to figure out what's good or not. Collecting items takes too long, but if you suffer at all from the normal level of gamer compulsion, you won't be able to stop. The crafting is just a lame waste of time that makes the game easier for players who don't need it to be any easier. Inventory management is a bitch. You have too much gold for all but the most expensive items to matter, and in any event you never need them. Combat is easy but requires some micromanagement and is so epileptically sparkly that, unlike PS:T, you can't just sit and enjoy the show.
Graphics are theoretically decent, but are often ruined by the shoddy camera and other glitches. Most cutscenes will have the camera facing the wrong direction or a companion standing in its way, so dramatic speeches will usually be accompanied by a mephit flapping its wings and shaking its ass in your face. The ragdoll equipment means that your character will be wearing a poncy hat or a silly mask, that you'll seldom see your companion's faces for helmets, and--due to spell effects--when you do they'll often be blotchily textured stone. All this combines to undermine the character's depth--when you actually get to look at two characters conversing, the graphics provide a surprising benefit that is lacking in the usual mephit-ass radio play.
All this combines to create an enormous series of impediments to what is one of the best series of RPG dialogues I've yet played. While I think PS:T has a better story (and MOTB is also largely derivative of PS:T), MOTB may actually be better at providing dialogues with interesting skill checks and meaningful consequences. The writing is stellar, the plot is strong, the characters are rich and interesting. Especially, though, the ways in which you can interact with people, the cleverly hidden options, are all wonderful. All this combines with really great voice acting that sells the characters very well.
It's a real shame that the game wasn't put together better. With a good camera and combat at KOTOR quality (which is to say, terrible but tolerable), without the loot whoring and load times, it probably would be tied with Fallout and PS:T for my favorite RPG ever. As it stands, it's a significant notch below those.
Bottom line, you should probably play.
I'm also going to go out on a crazy limb and suggest that you use a character editor to give yourself a pile of fat loot for all your party members and then just ignore the treasure along the way. But I'm sure people will get indignant at that suggestion. . . .
--EDIT--
As to whether to play NWN2 OC first, I don't know. I did, and it was really painful to get through (especially the first third), but the MOTB experience is noticeably better for having played through the OC. Characters from the first game have a role in the second, and the protagonist's arc spreads through both games in a meaningful way.
