If we are being honest here, Tron doesn't hold up at all. Tron was made in a time when only the wealthy had computers and only MIT grads had more than rudimentary knowledge of how a pc actually works. This allowed the film makers to take some *ahem* liberties regarding computer functions, networking ect....
In terms of plot, Tron is the silliest computer movie ever made. If you can get over that then it's a great film, but if you can't (and many people from the younger generation can't) then it's just stupid.
The graphics... with the rose colored glasses removed, are questionable as well. The special effects hold up quite well, but the cheap body suits look pretty dated, especially in HD. The compositing techniques used to merge the FX with the film footage is pretty horrible in a few spots as well.
I liked the movie, and still do, but I was around when it came out and understand just how cool it was by 80's standards. I can certainly understand why younger people wouldn't like it though.
That being said, it really seems like a dumb move on Disney's part to pull the dvds. I mean wouldn't a Tron sequel be made to appeal to.. you know TRON FANS?? If the original film is so bad in their eyes then why in the world would they make a sequel?