We aren't talking about the Neverwinter Nights released by Bioware in 2002 but the online only game offered as a part of America Onlines games area around 1997.
Neverwinter Nights was one of the first graphical online RPG's I ever played. It was very much like one of the 'Gold Box' games (single player computer RPG's based on Dungeons and Dragons and/or the Forgotten Realms which included titles like The Pool of Radiance and Curse of the Azure Bonds among others). The game mechanics followed the rules laid out by the Pen and Paper Dungeons and Dragons game and the world was essentially one large dungeon which you explored in a top down view moving square by square until combat started. A couple of the more unique attributes of the game were it's turn based combat and the way PvP evolved.
Play in NWN was turn based rather than real time. Weather playing against the computer AI or another player one person would submit their move and it would be executed then the other player or AI would do the same. If one person took too long to enter their move their turn would eventually time out and they would end up passing. It was pretty frustrating to fight against or alongside someone who took too long to take their turn but it worked out OK most of the time.
The other unique aspect of the game was PvP. The turn based mechanics applied here as well which made pvp more closely resemble a variation of chess than what you would find in any current MMO. The game was also very well balanced for PvP. I don't recall any particular class having any great advantage over the others and there was one more element that made PvP still more challenging: Monsters. Monsters became an integral part in most PvP battles. The challenge was to get the monster to attack the other player while avoiding it yourself. This added a third, unpredictable, element to the pvp game which really made it stand out from anything else available at the time.