Honestly the fact it had any CGI was groundbreaking. We take it for granted these days how easy CGI is, but at the time Tron was made movies were still recorded on physical film and most computer monitors were 480P resolution at best. The movies in the 70s and 80s that had "digital" displays like the terrain map in Aliens used some really clever tricks to fake things that would be utterly trivial to do today but were almost impractical to do back then.