Coming from someone who has played it for 6 years since its release without tire, this is one of the best RPGs to date.
So just imagine my joy when Shadows of Undrentide and Hordes of the Underdark, the two expansions for Neverwinter Nights came out! Twice more I was thrown into the wild world of Faerûn, but luckily at different locations and with totally different (yet still as amazing) stories. I won't delve deeper into either of them since this is a review for Neverwinter Nights specifically, but they are a must have. Not to mention most fan made modules use tilesets, sounds, creatures, etc. from both Shadows of Undrentide and Hordes of the Underdark.
Speaking of modules, with Neverwinter Nights comes a toolset, monikered the Aurora Toolset by Bioware, after the engine that is used for the game. In it players can make campaigns themselves, since they have everything that Neverwinter Nights has to offer at their disposal. Basically, it's just a huge sandbox world for the fans to create and share their creations. Many fans have made modules that are arguably better than the original campaign, by making the best possible playing experience out of the script implanted into the toolset (which is a variation of C) and some even going beyond that. Not to mention that Bioware has released a number of 'Premium Modules' (6 to be exact, all made over the course of the years, with Wyvern Crown of Cormyr being the latest and final module), created by Bioware themselves. Every one of these modules are very good, and definitely worth the $10 they each cost.
To add onto the awesomeness of this seemingly endless work of art, Neverwinter Nights has a multiplayer feature. In this, there is a huge collection of persistent worlds fan created, and despite it been out for 6 and a half years now, a good amount are still very active. Like any multiplayer community there are always a few idiots, but in my multiplayer playing time the consensus of personalities seem to be very positive and helpful.
There really is absolutely nothing that I can argue with, or criticize. Perhaps my only complaint is that Bioware stopped the production of Neverwinter Nights and handed it all off to Obsidian to continue with Neverwinter Nights 2 and future NWN2 content. That really was a letdown for me, but thankfully gameworlds and the almost infinite amount of player modules keep this game alive even to this day.
So what are you waiting for? Get some cash, a bag of chips and a drink or two, turn out all the lights and be ready not to step foot out of your house for months!