I own the Platinum edition of this game, and I'd be willing to buy it again here for the extras and for the Mysteries of Westgate campaign. Four campaigns (hundreds of hours of content), hundreds more downloadable adventure modules (see Neverwinter Nexus and Neverwinter Vault), multiplayer and DM-led game support, persistent online worlds, and a toolset and wealth of custom content to create your own adventures. If you liked Dragon Age: Origins or Baldur's Gate, definitely try this game. Despite some finicky camera and movement controls (some of which is alleviated by its extensive customisability and user-made fixes, such as Skywing's Client Extension), this is one of the best modern RPGs around. The major things that differentiate this game from its predecessor, Neverwinter Nights 1 (aside from the graphics), are the party system and dialogue system. You get a fully controllable party here, as you have in DA:O and the Infinity Engine games, while in NWN1 you can only directly control the main character. The second expansion added the ability to choose any of your party members as the speaker in a conversation, so that your main character doesn't have to be the one with all the social skills. (Mods exist to apply this functionality to the previous campaigns as well.) This is my most often-played game, and I bought it two years ago. I can't recommend it enough. If you love those other games I mentioned, you should also love this one.
Alas, GoG, your sale came too late, as I already purchased this during the Steam sale for the same price, and I'd much rather have had it from you, with your ideal approach to DRM. For those who missed it, I suggest you buy it here. I've been enjoying it for nearly a month now. If you like space combat with resource trading, escort missions, and other odd jobs to make money while going through a story at your own pace in a nice-looking space environment, you should enjoy this game.