The film succeeds on more levels than it fails, and far from being terrible, it is absolutely wonderful to behold. The visuals are breathtaking, the sounndtrack (By French dance duo Daft Punk) is remarkably well crafted to fit in with the onscreen action and the CG effects wonderfully intergrated with the live elements, but it's not quite the astonishing film that it could be. The reason for this lies squarely with what feels like an underdeveloped script.
Jeff Bridges puts in two very impressive performances as both Kevin Flynn and Clu, while Garret Hedlund and Olivia Wilde aren't given a great deal to work with. Hedlund and Wilde, as Sam Flynn and Quorra, are well cast and put in an admirable performance, but the material itself isn't all that it could have been. This is a shame, as with some better dialogue and some more depth to the characters (other than Bridges/Flynn), Tron Legacy could possibly have been one of the greatest science fiction films ever made.
One particular plot-thread that is very compelling and fully realized is that of the reunion of father and son Kevin and Sam Flynn is nicely handled, and latches you onto the characters well. The special effects for the film are beautiful to look at, and the kinetic cinematography is awe-inspiring, but I'm thinking that perhaps they made it a little too perfect. One of the strengths of the visuals that the original TRON was their simplicity.
Technology aside, the visual impact of those stark, cold digital worlds in the first film were dreamlike and almost magical. In this sequel they seem too refined, too detailed and too real. That's not necessarily a bad thing, but in the context of the TRON story it sort of defeats the purpose of the digital world. The scenes amidst the arena in the digital world are stunning in their imagination and execution, but you do need more that action. You need to care. Niggles aside, TRON LEGACY is entertaining, breathtakingly beautiful to the eye and boasts a superb soundtrack, so while it lacks character depth, it does provide an excellent way to spend a couple of hours.