Props to Noe for using some interesting techniques (Infrasound, strobing, some good camerawork) but the dialogue was utter shite and I found myself feeling extremely bored for the majority of the film.
There were certainly some aesthetically impressive settings (The Underpass and 'The Rectum') but that's not enough to save it, imo.
Apparently, all the dialogue was improvised because Noe only had a 3 page draft for the film. That explains a lot.

I got the impression he had no idea what he was doing for the majority of the film. 5 minute scenes of waving a camera around in a dark alley or club isn't very impressive or engaging.
I'll watch it again, sometime.