Neverwinter Nights works fairly well with Wine, but there is also a Linux native implementation.

Download this file:
https://docs.google.com/file/d/0B5kNyXljdFKganEzVDRrNGdKaEk/edit?usp=sharing

Install the game with Wine and unpack the tar.gz in the installation directory.
Go in the installation directory and check the installation files.
./fixinstall
If it succeeded you can play with ./nwn

OLDER METHOD, still available if the new one does not work.

In order to use the native version you should download those four files:
English_linuxclient169_xp2.tar.gz
nwclientgold.tar.gz
nwclienthotu.tar.gz
NWNEnglish1.69HotUUpdate.exe

Once done, follow this how-to. Here is md5sums for reference.
b021f0da3b3e00848521926716fdf487 English_linuxclient169_xp2.tar.gz
0a059d55225fc32f905e86191d88a11f nwclientgold.tar.gz
376cdece07106ea058d42b531f3146bb nwclienthotu.tar.gz
2213f9dae125fcda4196da03ebeedebb NWNEnglish1.69HotUUpdate.exe
9e5aec8eb2a8bea2626a51d36e72d12e setup_nwn_diamond-1.bin
ba9ed46b94eb84870e9e41eeab653859 setup_nwn_diamond-2.bin
5e07fe97815bf329eacd1f0a474128cc setup_nwn_diamond.exe

1- Download all the files and check the md5. In this how-to we assume you put them in ~/nwnlinux
2- Set WINEPREFIX to an non-existing directory and XDG_DATA_HOME to "$WINEPREFIX"/env (in this how-to we assume that the wineprefix is ~/wine);
3- execute `winetricks sandbox'. It is not necessary, but if you do you are sure wine won't install anything outside WINEPREFIX (i.e., icons);
4- Using Wine execute the GOG installer and install nwn somewhere (in this how-to we assume c:\nwn). After the installation execute also the official windows 1.69 patch;
5- create the linux installation directory (~/nwn in this how-to);
6- get the game data from NWN Wine installation:
$ cd ~/wine/drive_c/nwn
$ mv ambient chitin.key data dialog.tlk dmvault hak localvault modules music nwm override saves servervault texturepacks xp1.key xp2.key ~/nwn
7- unpack the three tar.gz files you downloaded, follow the order:
$ cd ~/nwn
$ tar xzf ~/nwnlinux/nwclientgold.tar.gz
$ tar xzf ~/nwnlinux/nwclienthotu.tar.gz
$ tar xzf ~/nwnlinux/English_linuxclient169_xp2.tar.gz
8- copy the key.
$ cd ~/wine/drive_c/nwn
$ cp -v nwncdkey.ini ~/nwn
9- Use the Bioware script to fix cases and verify playability.
$ cd ~/nwn
$ ./fixinstall
10- delete WINEPREFIX folder (await a little if you want the toolset)
$ rm -rf "$WINEPREFIX"

It should be it, ./nwn should start the game.
If it does not ensure you have 32 bit verson of libgl, libstdc++5 and
sdl_mixer and that direct rendering is working.

The toolset need to be used via Wine, so copy it too,

cp -vr nwmain.exe nwn.exe nwconfig.exe nwloader.exe nwserver.exe nwtoolset.exe nwupdate.exe Mss32.dll utils ~/nwn

set WINEPREFIX to a subdirectory of ~/nwn; we assume ~/nwn/wine and create the environment.
$ wineboot -b

Make believe you installed NWN in n:\
$ cd nwn/wine/dosdevices
$ ln -s ../../ n:

Create a .reg file with this content (ts.reg):

REGEDIT4

[HKEY_LOCAL_MACHINE\Software\BioWare]
[HKEY_LOCAL_MACHINE\Software\BioWare\NWN]
[HKEY_LOCAL_MACHINE\Software\BioWare\NWN\Neverwinter]
"Flavour"="Retail"
"GUID"="{7C503E58-B2BC-11D5-978A-0050BA84F5F7}"
"InstallType"=dword:00000002
"Language"=dword:00000000
"LastInstalledVersion"=dword:00000003
"Latest Installed XP"=dword:00000002
"Latest Installed XP Name"="Neverwinter Nights: Diamond Edition"
"Location"="N:\\"
"Version"="1.69"

[HKEY_LOCAL_MACHINE\Software\BioWare\NWN\Underdark]
"GUID"="{06C563F3-4403-449C-9D90-B29D755D6927}"
"Location"="N:\\"

[HKEY_LOCAL_MACHINE\Software\BioWare\NWN\Undrentide]
"GUID"="{B81ED410-73E2-471D-99CD-D7542B2F42D1}"
"Location"="N:\\"

Add it to the registry:
$ wine regedit ts.reg

And here it is, the toolset should be work as long you set WINEPREFIX
to that subdirectory. You might want to do a script that sets and executes.

Few more passages are necessary if you want movies or you want using
NWN in a multi user environment with separated settings and savegames.
But I will write about it only if there is request.