JohnnyCashed has put me in the unenviable position of having to defend this movie. I'm going to rise to the challenge, because I really liked it. However, in defending it, I am forced to admit up front that much of what JC says in his scathing review above is absolutely true. There are some errors in the spoiler flow, but really, he's pretty much got it.
So why am I defending it?
Because unlike him, I enjoyed it. I saw it twice, and enjoyed it both times. I admit I'm not normal, but even so, I think this means that there is a group of people who will enjoy the movie, just as JC's review shows there is a group who will not. So, just in case you're in my club, here's my take on it.
First, I want to respectfully correct some things JC said above. One of the biggest reasons to hate the TRON movie or movies is that they really make very little sense from a consistency or plot coherence point of view, it is true. So it behooves us to make sure that the reasons we take them to task really are reasons. With that in mind, SPOILERS FOLLOW THICK AND FAST as JC has set the bar low.
First, Kevin Flynn's past. Yes, he was a codebanger whose work was stolen. However, JC complains that despite becoming CEO he had time to write two video games and an OS in 1982. This isn't quite correct. At the time of the first movie (1982), Kevin Flynn was no longer an employee of ENCOM. He had written one game (which, graphically, is pretty rudimentary) called Space Paranoids, which John Dillinger, CEO of ENCOM, had stolen and passed off as his own work and which (at the time of the first movie) was already Encom's biggest hit video game. By the time he 'disappears' in the second movie, he has personally written at least one and maybe two other things. He has written the video game TRON, which we see Sam Flynn play in the arcade, and he has written and/or project-led the creation of something called FlynnOS. Well, this isn't all that unlikely - he disappeared in 1989, leaving him seven years to do those two things while serving as Encom CEO.
Second, the Programs and the System. JC is quite correct - one of the most jarring things about this movie is that when Flynn tells us backstory, all the background we were shown in the first movie is missing, and Tron is there. Wha? Well, Flynn does explain this. He explains that he set out to build a "new System" and that the only thing he brought with him from 'the old System' is Tron. He didn't write Tron, his friend Alan Bradley (Bruce Boxleitner) did, and Tron and he 'saved' the original system from the despotism of the MCP and its minion Sarc, both apparently avatars of the villain John Dillinger, then-ENCOM CEO. Kevin Flynn did write CLU (in fact, the first Program we ever see in the first TRON movie is an early version of CLU, who gets derezzed by a Recognizer controlled by the MCP in an unsuccessful cracking attempt by Flynn). In this movie, we are shown Kevin Flynn creating a new version of CLU. He, CLU and Tron set out to build 'the perfect system.' Why a new one? Well, as we can see in the 'real world' sequences of the movie, rather than being at play in the fields of ENCOM logic, Flynn is instead working on a smaller (but probably just as powerful) computer system that he has stashed in the basement of his arcade. That's the machine that's been running for 20 years when Sam finds it. It seems that it's not connected to the Net at all (which makes sense, as it's been developing in isolation, and CLU is obsessed with 'getting out' of it). This in turn causes trouble, though - it must at least have a modem, because CLU manages to page Alan from within it. From a phone which has been 'disconnected for 20 years.' Um. So...okay.
The Portal. This is problematic. Yep, the way the movie sets things up, Kevin Flynn liked to come slum around inside the computer without ever bothering to code a means to trigger the portal/laser sequence from the inside. Um, lolwut? On the slightly-more-consistent side, the whole disc conflict isn't quite as confusing as JC makes it sound - basically, Flynn has set up the Portal so that only a an entity which carries his ID token (the disc) can activate the portal sequence - so the whole Flynn's-disc-as-McGuffin bit is actually relatively consistent, especially for this movie. On the other hand, while I can see that leaving the portal running all the time is not a good idea, would you repeatedly descend into a giant dangerous cave system if you knew that the rope that got you there would automatically pull itself up after 8 hours, and you couldn't call out? Hell, I wouldn't.
A digression. JohnnyCashed brings up an important point about this movie, one which apparently (and quite understandably) causes him great grief with the film. Namely, TRON: Legacy is trying to walk an awfully fine line between sense and bullshit in the following manner, and failing. The film is asking you to simply accept a great deal of things as true which happened in the previous film ("You can digitize humans with a laaazer pew pew!", "Flynn controlled ENCOM when he disappeared," etc.) On the other hand, the film desperately wants you NOT to ask ANY of a large number of questions that their explicit sequelization of the first film brings up - and asking these questions can easily wreck the movie. I'm going to lay out some of them here.
Big question - what the hell happened to the previous system? When TRON ended, Flynn and Tron and Yurei had 'saved' the system, vanquished the MCP, and restored freedom. Why is Flynn screwing around with this new blank system? Or at least, what the hell happened to the one he saved? He says he brought Tron from the old system - what about all the other programs? What about, at the very least, Tron's 'girlfriend' Yurei, the counterpart of Alan's real-life sweetheart? For that matter, where the hell is she in the real world, if Alan is still around?
Another question - Why is Flynn so limited on the inside? If I ever have a chance to go into a computer system, I'm not going unless I'm firmly in sudoers, and have some handy secret setuid scripts hidden on my person. Flynn has some power - he has his own version of the Jedi Mind Trick, and can 'damp out' activity near him, apparently - but other than that, he's sorta just this Dude, man. I suppose we are to assume that when CLU rebelled, he 'took' Flynn's superuser bit, but...still. And yes - Jeff Bridges for some reason has gotten Flynn and the Dude horribly confused, and I frigging hate The Big Lebowski, so that was a real problem for me.
Acknowledging JC's point - How the hell old is Sam Flynn? The movie claims he was twelve when Kevin Flynn vanished in 1989, which means that they have retconned him and his now-dead mother into the story - because in 1982, Kevin was sorta mooning after Alan's girl (the human Yurei, and what the hell happened to her?) and there was no mention of any woman, much less the mother of his child. Whoops. I guess Sam being seven, as old as he could have been if he was conceived after the first movie (really, six, actually) just wasn't enough.
Okay, okay, enough. Let me finish on a different note. Namely, what is there to like about this movie? For me, an awful lot. As I have been trying to make clear in a muddled fashion, this movie is indeed broken in many ways. In fact, it's broken in almost the exact same ways its predecessor was. However, in my opinion, the brokenness is only about 1/5 as bad as in the first movie, and while the 'newness factor' which redeems the original isn't there, it is replaced by a nostalgia-fueled cool factor. This is, indeed, a sequel to an old and dearly loved childhood flick. It has some cool effects (like the first). It is a neat idea (like the first). It tells us what happened (sort of) to the characters we last saw 22 years ago. The soundtrack is frigging awesome. The visuals, while not necessarily breakthrough, are certainly well done, and are loving homage to the original. There are broken bits and question, yes - even Penny Arcade checks in on that one - but it's possible to enjoy this movie despite them.