Two major components to this review: structure and impact. I will use inline spoiler tags, but note that I do not consider facts about the true events to be spoilers. It's a biopic—we know what happened. But if you don't, be warned that I will "spoil the ending", as it were, and stop reading now.
This is an important story. We all know what happened to the plane, and we all know what usually happens to aircraft whose pilots attempt to do what Sully pulled off. The story of the cra— I mean, forced water landing, itself is amazing. The whole process is so incredible, and this movie captures everything from the initial bird strike through the last boats carrying passengers to shore. I thought the story of the landing itself was done very, very well. This movie is worth watching on the strength of that portrayal alone.
I did have some major objections to the structure, though. They're probably not unlike @LuckyNumber78's complaints…though I'm not coming at this from the perspective of a screenwriter, just as a viewer.
Specifically, the most insulting sequence in the entire film to me was the beginning, which seems like it's throwing us right into the narrative, but turns out to be a just a dream (if it wasn't given away already by the aircraft trying to fly through Manhattan, grazing skyscrapers on its way to a fiery crash). That put me in a pretty skeptical mood for the rest of the film, and for good reason—lots of sequences turn out to be Sully's daydreams/hallucinations/imagination. They were not managed well, in my opinion. That's not to say I object to their use; just that they weren't done well in this film.
The whole temporal flow of the film is pretty unhinged, actually. Though it technically follows a single event from start to finish (the NTSB investigation), even that continuity is disrupted in places. The film retreads certain events, and includes a few others, for no discernible dramatic purpose. And even when it does buckle down and get on with settling the NTSB investigation once and for all, the climax reeks of half-assed attempts to make it "Hollywood suspenseful" that just fall flat. (I mean most of the final NTSB hearing, if you're wondering, where evidence like the report on the left engine shows up at the last minute.)
To be quite honest, I waffled between a 5 and a 6 on this one, not because I didn't find the film compelling, but because it doesn't work structurally. I get that there's an element of metaphor in how the film is laid out, and I appreciate it, but for a film like this it's really not in the story's best interest to keep the audience guessing at what's real. I finally decided on a 6, but only because the true story deserves more than a 5.