I've re-watched the original Tron on occasion over the years, and just recently last week in preparation for the new movie (which I haven't seen yet, because every theatre in my city has it in headache-vision only, but that's another rant).
Maybe it's just me, but I find it holding up less and less as time goes on. The first part of the movie is cut very poorly and frequently jumps around for no real reason. Once Flynn is in the Tron world, the movie ever-so-slowly gets rather tiresome and boring. Now, part of this is me just being used to modern movies that have a much quicker pace overall, but it's more than that. There really just isn't all that much story here. And all of it is hurriedly explained in the first 15 minutes or so, so the rest of the movie is just a Lord of the Rings style quest without much actually happening.
Now, visually - I'm one of the few that still think the effects hold up. They just have a unique look to them that really exists in no other movie of its time or any time. It always surprises me upon re-watching to realize just how many computer graphics were used. Knowing how much effort when into them, I always think there must only be a few shots, but it never ceases to amaze me just how often you see them. Plus, the costume effect is just something we'll never see replicated again.
If it's on in the background on mute, Tron is a pretty cool movie still. But actually trying to watch it? I'm just as likely to fall asleep somewhere around the 45 minute mark as not.
Not sure how much this will be considered Flamebait on Slashdot :)