Have you tried to watch the original Tron recently? I was first exposed to the 1982 film several years ago. I think I got through it that time, but barely, and can’t claim that it left enough of an impression on me to actually remember anything heading into a recent re-watching.
Watch the trailer. Yeah, it’s pretty much like that. A goofy, very eighties plot stuck on top of a compelling concept, some interesting (for their time) effects, and a truly unique style. That formula apparently worked well enough for the film to develop a fan base and survive in popular consciousness. Thus, with the potential for profit on the line, a sequel was ordered up.
I won’t attack Tron: Legacy for being unnecessary, I think there is enough in the original to draw out a compelling continuation of the series, and any use of the license would surely be better than the likes of Yogi Bear. I will, however, attack it for being an unnecessarily direct sequel. The original film may have worked in its time, but going back to characters from some 28 years ago, when those characters are not the part of your source material which are iconic or well remembered, makes for unnecessarily awkward storytelling.
The problem with Tron: Legacy is, put simply, the plot. For whatever reason, the decision was made to remain beholden to the original film and make this thing as a sequel, where a re-make/re-boot/re-imagining would have better served to bring the world of Tron to modern audiences in a more engrossing way, unencumbered by the events of a film most people don’t really remember anyway.