The issue is that Nar Shaddaa was always an awful, dirty place. In the KOTOR games it was one of the planets you visited, and was nowhere near as neon-shiny as it is in this game.
I think Mako put it best, "Looks like they added more lights to hide the grime." The Hutts polished up the moon's surface with all the glamor and lights to make it more appealing to the less knowing traveler. As for the other areas, they still give off the "wretched hive of scum and villainy" atmosphere that it reeked of back in KotOR and Dark Forces. Which makes perfect sense because the Dark Forces series took place in the deeper parts of the city moon, and Kotor 2 took place in the refugee sector. So in the end, whether Nar Shadda was grimier or just as clean on the surface as before. It's as gritty and dirty as I last saw it where I was before in the other Star Wars games.