For Walt Disney Pictures itself for commissioning this film. Remember, at the time of this film's production, the company was sinking even more into irrelevance as George Lucas and Steven Spielberg seized the culture zeitgeist the way that Walt did in his prime. Furthermore, the company's one attempt to imitate them, The Black Hole, proved an embarrassment in 1979 and their animation department was barely surviving with new talent still suffering the loss of Don Bluth and his team and vision. Out of this despair, the company was approached by Steven Lisberger on this idea for a film with a radically different look with revolutionary visual effects technology, and took a chance in saying "yes" to producing it. Maybe it didn't work out all that well, but it was a gamble worth taking and a Cult Classic franchise was born regardless (albeit after the fact).
And the fact that so many little (and not so little) kids looked at this and went "Cool!" Then, some of those kids went on to found Pixar, including John Lasseter, who stated during the "Making of Tron" feature on the DVD that "without Tron, there would be no Toy Story".
Also the fact that this was something of a "coming out" album for Wendy Carlos after her gender reassignment surgery.
As for the movie itself:
The Light Cycle battle. Arguably the most famous sequence from the first film, making the Light Cycles the coolest bikes ever on film, and done with such incredible detail and pacing that it holds up thirty years later.
For this troper when he first seen the sequence, he was amazed at how fooled he was. At the start, it looked all bulky when the cycles only turned the 90 degree angle. This troper thought it was all they could do. Then the escape sequence, when the bikes now started moving more fluidly like they were real motorcycles.
Dumont's "Defiant to the End" approach to the guards. After telling Tron and Yori that he's been in the system too long to really believe their plan can work, and that so many "brave plans" failed before, he ends up relenting. While the MCP is putting him through Cold-Blooded Torture, he still has it in him to mouth off to Sark.
Dumont: (in obvious pain) What do you want? I'm busy!
Sark: Busy dying, you worn-out old excuse for a program?
Dumont: Yeah, I'm old. Old enough to remember the MCP when he was just a chess program. He started small, and he'll end small!
The scene where Tron makes contact with Alan. You hear through the film that Users are to the Programs what Gods are to us. The bright light, and the sheer joy on Tron's face drives home the analogy.
Flynn's Indy Ploy in making a brand new path for the Solar Sailer to traverse, escaping the Recognizers hot on their tail. How does he do it?
Flynn: (still dizzy) Elementary physics: a beam of energy can be diverted. Are we there yet, mommy?
Sark grows 50 feet tall for the final confrontation. Tron doesn't miss a beat and splits his head open with a disk.