It is said that art is a mirror; your view of the subject informs your opinion of the art. Surveying the critical reaction to the film, the saying is true.
One of the criticisms I heard is that the movie doesn't describe the characters. Actually, I think that was the movie's point.
The movie starts out, after its initial introduction, with standard airport scenes. A lot of travellers in an airport waiting area, the pilots doing their walkaround, the stewardesses arriving and preparing the plane. Air traffic controllers are managing a typical morning travel rush. The Air National Guard is preparing to run an exercise.
In other words, it was an ordinary, typical late summer day. Just like September 11th, 2001 was.
And the movie is about ordinary people, who find themselves thrust into an unimaginable nightmare. It is the story of their response, as the air traffic control tries to figure out what is happening and the military tries to respond, despite poor communications and bad information, and the precedents that were shattered.
One thing I was reminded of was just how shocking it was that a hijacked plane was used as a weapon. In all previous American hijackings, the target was the passengers, and the plan was to ransom them. On September 11th, the planes were the targets, and the hijackers intended to use them as weapons. It was a dramatic change, one we simply were not ready for - and the resultant shock enabled the hijackers to successfully complete their suicide missions.
Except in the case of United 93. That flight had been delayed, and the hijackers had waited; by the time they had turned back over Pennsylvania, the passengers had figured out what was happening and did something about it.
And they were just ordinary people. People like you and me. It could just have easily been us - which begs the question: Could I have done that?
In the end, your view of the movie will depend on what baggage you bring with you into the theater.
I do recommend you see it, if for nothing more than to remember that day and the heroism of some ordinary Americans.