I like it. It's one of my favorite planets.
I'm not a big EU expert, but I think the time period is a factor in the shinier version of Nar Shaddaa we see in SWTOR. The Nar Shaddaa you may have read about in a novel was most likely set hundreds or thousands of years later, plenty of time for a Vegas-like NS to fall into total despair. It makes more sense that it was once a successful, prosperous place that fell apart over time than if it was always the same.
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.