I'm not going to explain much about this movie story/premise, because I assume most viewers were fans of the original Tron.
When I first heard about this movie, I couldn't be more excited: an old movie with brand new technology? Even if the story turned out bad, it was a new Tron, and that alone made it perfect.
I watched the movie last night, in 3D, and it was a very pleasant experience for the most part, but don't think this is a great movie, because it's not.
Flynn (Jeff Bridges) is back, and in two shapes. An older Flynn, and a computer generated younger Flynn. The computer model looks good (for the most part), and it was necessary, otherwise we would have ended up with an old man with a ton of make-up on it's face, just to shave off a couple of years.
The movie starts with Flynn disappearing, and his son entering the Grid world in search of him. It's textbook script, but then again, what could we expect from Tron? It was never about the story, and this movie proves it. The plot is weak, and weakened by poor/unnecessary dialog and very shallow characters.
Luckily, none of that matters once the Grid world is shown to us. Visually it's great, and the action scenes are fun and fast-paced. I even dare saying it's the best 3D movie I saw so far, which also poses a problem: this movie looks great and feels great only in 3D, and in the theaters. I can't imagine myself in a few months buying the movie to watch in my sofa.
Another problem with the movie is that half-way through, it becomes repetitive. Maybe if they kept the action flowing, with little dialog, this movie would have been better, but trying to add depth to such a poor script ends up boring the audience.
The bottom-line is: Tron Legacy if fan-service. It a re-rendered universe with very little story, but very good looking.
7/10 if you watch it in the theaters, in 3D 4/10 anywhere else