I saw the original TRON back in 1982, and loved it. This one is a worthy sequel, made with a lot of respect for the original.
In the original, Jeff Bridges played Kevin Flynn, nemesis of evildoers at ENCOM, a computer company. The bad guys arranged for Flynn's abduction into the Grid, a cyberworld where program fought program, gladiator-style, all under the dictatorial thumb of the Master Control Program, or MCP. After many close calls and exciting conflicts, Flynn's real-world self was reconstituted, and the bad guys (and programs) were defeated.
In this movie's prologue it's revealed what happened next: Flynn and his buddy Alan (Bruce Boxleitner) took over ENCOM. Flynn got married and had a son, Sam, but still commuted back and forth from the Grid, engaged in world-changing research. But one day Flynn doesn't make it back.
So Sam grows up and 20 years later or so, he has become a bit of a rebel; like father, like son. One fateful night, he's lured back to his dad's old video arcade, and before you can say "I saw that coming", he's plopped into the Grid too. Soon he learns that the show's being run by CLU, an evil program that looks just like Dad—from twenty years back. And CLU lacks any kind of father feeling whatsoever. So Sam finds himself doing the gladiator thing with the deadly flying disks and the cool light-cycles, and—
In short, I was in nerd heaven for a couple hours. Everything I liked about the original, upgraded with nearly thirty years progress in computer graphics.
Consumer note: I wasn't too impressed with the 3-D. (The real-world scenes are in normal 2-D, with the Grid scenes in 3-D.) You might want to save a few bucks there.
What really impressed me was the whole process where they "youngified" Jeff Bridges a couple decades. It was stunningly realistic. If they can do that, it won't be long before they can do anything with cybernetic actors.
I found myself fantasizing about Casablanca 2, with CGI-resurrected Humphrey Bogart, Ingrid Bergman, Claude Rains, and Paul Henreid. Something like: Victor gets captured by the Nazis; Ilsa tracks down Rick and Louis and pleas for them to stage a rescue. After an initial "I stick my neck out for nobody, remember?" rebuff, Rick undertakes the mission…
OK, so that would be sacreligiously dreadful. But still.