I found the black and neon look in the sequel to be MUCH more visually striking.
I find it dull because it's so monochrome. The Grid in the original was not limited to just two colors. Only the characters were.
And the world of the original wasn't all that flat and gray. The few physical sets the actors interacted with, like the tank interiors, looked that way because they were filmed in black-and-white and the film frames were printed onto animation cels to be backlit for the "neon" effect. But the fully animated environments had a lot of different colors and were very vivid.
And plus, as we know from today's videogames, it's not that hard to simulate the natural world anymore. It only makes sense that something like that might pop up over there now.
But the difference is in thinking that the
purpose of computer animation is to replicate the look of reality. At the time of the original film, there was no prospect of that, so computer art and animation were seen as a means of creating entirely
new kinds of images, things that nobody had ever seen before, and expanding the horizons of art and animation. These days, it's all about copying reality, and that sense of embracing the new and abstract, of inventing and exploring new aesthetics that are impossible in reality, has been lost. On the DVD features of the original movie, one of its makers laments that change. They weren't trying to create a world that duplicated reality, but to create one that was entirely
unlike reality, that was as new and exotic as it could possibly be.
This is the fundamental difference between
TRON and
TRON: Legacy. The goal of the former was essentially to create a new kind of cartoon, to make the live-action elements look like computer animation and be as far from reality as possible. The goal of the latter, like the goal of all other CG-heavy films these days, was to make a live-action film incorporating computer-generated images that looked like part of a live-action environment. They're completely opposite design philosophies.