Probably one of the most disappointing experiences I've had. I was just expecting too much.
The game starts you off in a tutorial to explain the basics before starting on the four tasks of the first chapter. It only takes playing through the first chapter to see what is wrong with this game.
First problem I seemed to have is the party system. It's non-existant, in single-player mode at least. You can hire people to fight with you, but you have little control over what they do as they are AI controlled.
Speaking of AI, it's terrible. There were times where I was being attacked and the henchman I hired was just standing there watching. Sometimes I move on ahead and it takes him up to 10 seconds to start following me. The AI gets stuck behind bits of wall and doors as well and you can only have one henchman at a time.
The only other party element is the beasts you can summon with certain spells. In online mode I'm assuming this would be much better.
This leads onto the second problem, which is a total bore when it comes to fighting. Because you can only control a single character (pretty much), it doesn't leave a lot open in the way of strategy. For example, in Baldur's Gate you would have a party of warriors with different skills to get the job done, while here you have to make do with one character and if he can't do it, you're stumped. Sure it makes the fights quicker, but ultimately unrewarding and repetitive.
You find yourself caring less and less about the plot of the game because everything just sails by, nothing really hits you as different or unique.
Third problem is the technical side of the game. It demands a lot out of your system even though it provides less than spectacular visuals.
The water effects were broken and non-functional on my PC, using a mainstream ATI graphics card which just created a flickering, polyganal mess.
The walls in dungeons and in narrow areas are too tall and you often can't see what you're doing because it's hard to move the camera to a suitable angle.
Within my short time playing I was subjected to all manner of bugs, not including the appauling AI. For example, somehow it decided my character would walk up onto the black void atop the wall of a dungeon. Once up there, he could not move in any direction. Another example is that I had been given 4 charms to give to 4 wereolves. The problem being that the first one I found took the charm and turned back into a human, yet still retained the dialog of the werewolf. I had to go through the dialog again and give another charm to make him change the dialog to what should have happened on the first try (fortunately I had saved recently and so I loaded the saved game, started again and this time it worked on the first try).
Fourth problem is lack of open-roaming. This game follows a very linear path when compared to Baldur's Gate, in which you could explore pretty much any part of the world you liked. In Neverwinter Nights however, you are only allowed to play in the areas that are part of the storyline. It's also a shame that you can't really make use of the evil alignment either, because you can't kill many of the normal people and you never seem to get hunted by the law or bounty hunters or anything like that.
In my opinion, the only thing this game has going for it is the length and probably a decent multiplayer system. Actually giving it anything more than a 5/10 would be pretty generous since the only fun seems to come from 3rd party sources.