For me, though, plot-wise, the problem Legacy runs into is that it ultimately tells the story of a hero (Sam) attempting to save someone (his father) who doesn't want to be saved. In what should be an incredibly emotional if not triumphant moment, it feels like the plot comes to a screeching halt the second Sam sees his dad again for the first time… and his dad just isn't that fired up to see him. Which kind of kills the rest of the movie for me. IMO, it would have worked so much better if his dad had been trapped down there against his will, or held prisoner all that time, and then it essentially became a prison break/heist movie, with Sam trying to save his willing and appreciative father.
It's that, and the computer world itself not being fully explained or explored that knocks the movie down a peg or two in my book. I wanted to know more about the rules of the world, how sentient the various programs were, can they or Sam come back from being derezzed, etc. I really needed a couple of those Morpheus-explaining-the-rules-of-the-matrix-to-Neo scenes, where it's mixing exposition with training or action.
To that end, while the early "games" sequence is incredible to look at, it was way too convenient for me that Sam, having not even been in the computer world for 20 minutes, is either instantly a badass at everything, or gets by on pure, dumb luck. When a potentially better movie would have thrown him in prison with his dad, with the plot basically becoming Tron: Gladiator, where, as "slaves," it's Flynn training Sam in the ways of the computer world, while Sam has to compete in the games throughout the movie, all as he and Kevin are covertly working on a way to break out, maybe with the help of Quorra or whoever.
I don't know.
Just anything to better-serve the momentum of the plot and immersiveness of the world. Otherwise, as-is, it has a bit of Last Jedi-itus for me, where it's a protagonist spending way too much time trying to convince the old, reluctant, curmudgeon mentor to go on a quest, which just isn't that compelling or emotionally involving to me, plot or character-wise.
That said, keep the final act basically act as-is, because that "air" battle/chase sequence is awesome/incredible just to look at, and I do love the ending.