Are you guys actually trying the game or stopping at the menu screen?
The Menu screens and intro video do not scale. The higher the resolution, the smaller those screens get.
But once you play the game, it fully uses whatever resolution you set it to.
I have played NWN for more than a decade on everything from my old CRT when I got it, to a 30" 2560x1600 LCD at native resolution. It supports just about any resolution and aspect ratio.
Take a look at this video. It starts with character creation menus which are small and centered, but fast forward into the actual game and you will see it uses the full screen:
https://www.youtube.com/watch?v=FI25Ykcfhdc