Definitely a must see (of course I viewed it with a slightly skewed perspective...)
For me, being able to recognize (fondly) all the landmarks and bridges and street scenes made the whole movie more personal... especially the Port Authority Bus Terminal where the movie starts was like being in my neighborhood -- I've walked it so many times. My memories of NYC that day are vivid, but it was surprising how many of the scenes made me remember things I'd forgotten... A wonderfully told story with no politicking (a first for Ollie Stone). Worth seeing.
My only comments? Not enough dust... Not enough red (fire glow)... and not enough of the sense of community New Yorkers and the world shared that day (and for a time after) until too late in the movie. Don't wait for the DVD... it's worth seeing on the big screen.
JUST DON'T FORGET WHO BROUGHT THOSE BUILDINGS DOWN ('cause Ollie never mentions it)