I doubt there'll be a 3rd part. Too poor reviews, from what I've heard.
I saw the first Tron movie when I was a kid, and have watched it a few times since as well, so I'm one of the few who knew that Tron was actually a program and not the name of the world it all happens in.
There are things in the old movie that are silly as well, but that was 1982 and this is now. I really think they should have done a number of things differently in Tron Legacy. Too many things are just illogical, considering it is a computer, as you say.
For example, it makes no sense that Tron suddenly remembers who he is, just because he gets eye-contact with Sam. He had plenty of time to look at Sam during the games first in the movie.
And it's also silly that Sam appears in the grid world at a copy of Kevin's office, and have to exit way up in the air where "it's difficult to reach". Difficult to reach? They could all fly!
I can accept that the light-cycles now turn 360 degrees and are able to perform jumps - because of evolution or whatever you want to call it. But they can't leave the game grid? What? Ok ok... we can come up with an excuse for that too. Some players probably left the game grid a while back, so Clu made new rules that prevented them from doing so in the future. We can find excuses for most things, but I still think it's silly. It's like they've been discussing the plot: "Ok, so Sam escapes the same way Kevin did?"
"Yea, and then Clu and the other baddies follows"
"So how does he escape?"
"hmm... let's just say they can't"
"...can't? What? Why not?"
"....the bikes has to stay on the game-grid"
"How can Sam escape then?"
"Um...let's say he gets picked up"
But there are also things I liked. I recognized a few of the Linux commands when a character was typing in the console, and it's really nice to finally see some non-scifi regarding that part. (As opposed to the hacking-scenes in e.g. Hackers or Jurassic Park).
I also liked the many things they kept from the original, from the recognizers to the presentation of the identity disc, which was kept from the 1982 movie word by word.
And the music was great all the way! Sadly they over-used it. Even when the story was slowing down, the music kept on booming as if they were telling me "Hey, this is a great moment in the movie" - and I looked around to see where this great moment was hiding.
All in all Tron Legacy was disappointing to me. It's a thin predictable story, and it really deserved much more. It deserved much more thinking before it went into production.