This is an excellent film. Don't believe the haters.
I've been a Tron fan since the original movie released when I was nine years old. It was the first movie that I saw multiple times in the theatre. I probably saw Tron seven times with every friend that I could convince to go see it.
I will also be seeing Tron:Ares multiple times in the theatre. It is well acted, well delivered, and has a plot different from the first two films (touching on philosophical elements and transhumanism.) It is fun, musically excellent, visually excellent, and well written action film. The pacing is excellent.
It ties the franchise together well, while leaving the possibility of a reunion for all of the previous characters (and some new ones) to a future installment.
In short, go in with an open mind --free of negativity and expectation-- and just enjoy the film and be entertained!