I like both for what they are. No doubt Morrowind is a better game un-modded but NwN's easy to use editor has enabled a lot of custom campaigns that probably would never have existed without it. Plus, NwN had jiggly boob physics.
It's sad that single-player had to suffer like this to make multiplayer (without pause) usable. NwN does get a lot more playable once you find an item with a permanent haste enchantment.Neverwinter Nights is the worse of the two. Most of the game is wasting my time over waiting for the game to decide it's been six seconds so the character can finally do an action now. Often, if playing a melee character, combat boils down to you just waiting for the enemies to finally be dead while occasionally clicking to drink a potion. The only way to play a character that is somewhat active is to play a shadowdancer/assassin or wizard and even then, you have to put up with the shitty 6 second round timer to do actions. It would have been fine if you actually controlled more than one character like Baldur's Gate or Icewind Dale. But it's just slow boring dogshit for a single character game since it means that combat for anything above 1hd will tend to drag on longer than it ever needed to. Plus the thing where your character will dance around the map during melee, often walking into nearby traps, is retarded.
It's possible there are some engine limitations here that make fully sloped hills more difficult but this is primarily an issue with the shitty default tile-sets rather than the engine. Even with the default tile-sets there are slopes to go from one level to another and community tile-sets have expanded this to much more realistic hills, e.g. from a quick search:Bro the engine is barely 3D in practice, it's extremely blocky in layout and doesn't even support slanted floors and walls. Every angle is 90 degrees, hills are always separated from the lower level by a cliff rather than having smooth transitions, etc.