Hollywood often takes flak for needlessly rushing out sequels and remakes of perfectly good films, which is why I applaud the recent trend of producing bewilderingly belated remakes (Clash of the Titans) and sequels (this) to frankly terrible films.
Tron certainly didn't need a sequel. But what it lacked in plot and characterisation (and pacing, and coherence) it made up for with a strong visual and audio aesthetic. Nothing looked and sounded like Tron, it struck out in its own direction and its subsequent lack of commercial success ensured that nobody bothered to follow it. It stood proud and alone, an all-but forgotten time capsule of early CGI and 80's computer slang.
Tron 
Tron Flying Ship Thing Legacy is not a great film, but is does have some of the same styling has the original, perhaps wisely watered down for more popular appeal. It certainly looks fantastic, with sleek lines and imaginative action sequences. The characters are weak and the plot is simplistic, with an ending that is not so much telegraphed from the first act as teleconferenced with a detailed powerpoint presentation. But plot is not why people go to a Hollywood blockbuster, and Tron Legacy's 2 hours feel like the drumsticks in KFC Quarter Packs - tasty and they pass quickly.
The credits say that the producers commissioned Daft Punk to write the soundtrack for Tron Legacy, but honestly it could have been other way around - Daft Punk's whole career was basically an audition tape for this job. The traditional Daft Punk sound is augmented with an orchestra and it sounds great. Or maybe GREAT!, it sure is LOUD but a film this visual needs a strong soundtrack to go with it.
One of the things I am most enjoying about the recent crop of 3D movies is that directors are finally being forced to hold shots steady for more than 3 seconds. Action movies were becoming almost impossible to watch due to the incredibly fast cutting that seemed to be mandatory for any fight scene, it was bad enough in 2D but positively nauseating in three dimensions as audiences' eyes struggled to keep up. Despite the excellent special effects, Tron Legacy looks very old fashioned in terms of shot length and placement, with all the action happening safely mid-field, something that my middle-aged eyes find refreshing.
According the the IMDB, the same director is readying a remake of another terrible film with a strong visual flare, The Black Hole, for deployment in 2012. I am almost looking forward to it... (hopefully they manage to recreate the insane original ending.)
Tron Legacy : Recommended if you can see it in 3D