Overrated, but still a good CRPG based on D&D rules and Forgotten Realms setting.
Action part of the game is probably the strongest part of the game. Point&Click style of Diablo is combined with tactical pause of Baldur's Gate and enhanced with great animated combat moves. Neverwinter Nights was the first 3D game I played that had animated parries, dodges and projectiles (arrows and bolts) that stayed in their targets after they struck. The only complaint is about tactical options in combat. Pause key is not of much use if you don't have sufficient control over your henchmen, companions and summoned creatures. The companions will fight on their own according to the advice you give them, like in Fallout and Arcanum, for example, but there are painfully few parameters to set for them. For example, henchmen who are told to use their ranged weapons will not switch to melee weapons even if they are surrounded by opponents. Another great problem is that there is no way to tell your melee-fighting companions not to charge the enemies except by constant right-clicking to open their context menus, which can really bog down the action gameplay. If you want to get through battles quickly, it is best to take Barbarian or Monk as a henchman.
The story of single player campaign is sadly disappointing. Cliche after cliche combined into a long, epic campaign of several chapters which all look alike. In each chapter, you will have a generic core area, with several generic shops and several generic NPCs who will give you generic quests. Generic is the keyword here. The core area is surrounded with 3 or 4 mission areas. You will have to visit each of these mission areas to finish the main quest of the chapter, but other more important quests will also be scattered all over these 4 areas. Voice acting is catastrophic, especially considering that Bioware was involved in development of true gems like Baldur's Gate 2 and Icewind Dale. The only exceptions are roles of Aarin Gend and Lord Never. If there was a mark for story, I'd give NWN 1.
Technically, the game is quite good. It spent a long time under development, just like its contender in single player area, Morrowind, but Bioware were soundly beaten by Bethesda. Neverwinter Night has great graphics for the year in which it was released, but won't get much opportunity to enjoy it. The only way to clearly see the detailed 3D object is to zoom in all the way, and to have a clear view of the area around your character you have to zoom out all the way. After a couple of hours of zooming in and out you will get bored with it and just zoom out and keep hacking and slashing. Code optimization also isn't the strongest quality of Neverwinter Nights. Whole areas are loaded at the time which means that scripts that execute all the time keep doing so even if they have nothing to do with your character at the moment. This can really slow down the gameplay on contemporary systems in busy areas like Neverwinter City Core and it doesn't shorten the loading times significantly. Still, computers have advanced enough for us to play this game comfortably these days.
Computerization of 3rd edition of D&D is quite good. All standard classes, races and feats are either 100% true to the pen&paper version of the game or logically converted to be equally useful in a computer game. Selection of skills and implementation of their use in the game are also great. This outstanding impression is marred only by scant selection of items in the game. RPG veterans will be stunned by how few types of potions and unique items can be found in the game. Those who explore the modding options will be even more shocked as implementation of some fairly common D&D potions and items that are absent from NWN is fairly simple.
All in all, NWN is a valuable game I'd recommend to all fans of roleplaying games, but it has shown that attempts to win both single and multiplayer market with one product will never win on either side. If you like the game engine but would like better story, more items and better henchmen control, I definitely suggest the expansions Shadows of Undrentide and Hordes of Underdark.