The original Tron was about a stoner-hacker named Kevin Flynn who gets trapped inside a computer mainframe, where all the programs look and talk and act like people, which at the time was how computers worked (tiny slaves inside metal boxes). It's kind of complicated, but basically he has to play a bunch of hilarious computer games involving motorcycles and frisbees, and then he defeats the bad program, and then he goes home to the "real world" where he invents the iPod and becomes a controlling autocrat known for his hatred of pornography.
Or does he? In Tron: Legacy, the title of which is written in a foreign language where the word "legacy" means "2," Flynn appears to have returned to the computer-world and become some kind of grizzled cyber-guru. There is also a program written by Flynn, who looks like Flynn, called Clu 2.0, and may or may not be "the bad guy." (I told you it was complicated! Computers are hard!) Clu is played by Jeff Bridges using some kind of witch-magick that makes him look about 35. It works pretty well, judging by the trailer.
Anyway, Flynn's fratty son (Garrett Hedlund, who you don't remember from Troy and Four Brothers) goes into the computer country and has to ride his lightcycle (computer for motorcycle) and have literal cybersex with Olivia Wilde (of The O.C. and House) and probably reconnect with his dad in some kind of emotionally satisfying way. Or whatever.
Will it be good? OK, well, it won't be as good as the original Tron, which as every cultured person knows is the best movie ever made about computers. And it's kind of a bummer that they seem to have just taken the (awesome) production design aesthetic from the original and made it shinier, instead of coming up with a new, equally awesome aesthetic—it's been 28 years since the first movie and a lot has changed with computers!
But it has Jeff Bridges, which counts for like a million points in a rating system I just made up. And Daft Punk wrote the score (I don't know if that's a piece of theirs in the trailer), which is also worth a million points. So it's already at roughly two million points, which is definitely see-it-opening-night quality. If you're a cultured person.