I honestly think NWN is one of the games that has aged best. The main campaign I can't tell much about, I don't even remember it. I think to have the feeling that it was okay.
That said, NWN was always about the multiplayer aspect, with how easy to build a world was as they provided the tools for it, tileset based world builder with scriptable everything… NPCs, items, transitions, sound, lightning, etc. You can do literally anything you want, the only limit was the amount of time you were willing to sink into it. I've seen pretty well done Star Wars mods in NWN.
The Enhanced Edition added modern resolutions, and many options to modernise the general aspect of the game, including reflections, contrast lighting, and such that make the game look pretty good (if obviously not AAA good).
The vanilla character models would look bad now, but luckily with the enhanced edition you can add hi-res texture packs that players don't even need to find manually to play the server, it gets automatically detected and downloaded via steam upon login. This is just an example of the first hi-res human head pack that came up on a google search -
It holds pretty well nowadays. It blows, say.. Age of Decadence out of the water, which is a pretty well praised modernish game. And there's the same for all kind of creatures, objects, props, scenario, tilesets.. and if there isn't, you can create it. Again, only limited by how much time you want to put in it.
I can say a lot of things about Neverwinter Nights, but not that it didn't age well. Playing the vanilla, non-enhanced edition without mods/haks, yeah, that doesn't hold very well nowadays, but that's not really what the game is today.