I think this got dismissed partly because the previous two films focused on beautiful images, whereas this one (completely by design) focuses on ugly ones.
Also because the first one (I still haven't seen the second) had more of an understandable structure. This, from what I remember, seemed more like a random stream of images. Also, while I love Glass, musically I think he's kind of past his prime. I mean this is good, but just not as amazing as Koy. Which was probably the best thing he's ever done for film.
I think I've mentioned on here that Godfrey Reggio is a good friend of my dad's, so I've met him and talked to him. (I have fond memories as a teenager of seeing Anima Mundi in his editing studio a few months before it actually released) I was always curious why all of the footage in this movie was not corrected for the 1:85:1 aspect ratio when he went through so much trouble to do conversions for all of the footage in his previous films. As a result, a lot of the film looks stretched which led many people to assume the DVD was wrongly mastered, but he claims he did it on purpose. I think, honestly, Reggio didn't want to bother this time around and felt it was a creative decision and I get the feeling he regrets it. Still, I think the movie turned out great for what he was intending.