So I've watched the movie twice, first in a standard 70mm film theater, and the second time in the Lincoln Square 70mm IMAX.
I enjoyed the movie the first time, the sound mix wasn't greatest, and I was a bit distracted trying to piece together the three timelines, not realizing they diverge post convergence. It was a really good movie but definitely wasn't top of my Nolan list.
The second time I watched it, it was no question that Dunkirk at least ties with The Prestige with the top spot for me. Even from the very first scene, the intensity of the movie easily racheted up many levels above the first time. It feels weird to say this, but this is also the most emotionally moving Nolan movie to me even though it doesn't dramatize the characters for you. The constant climax throughout the film makes every single situation and action much more piercing given that I already know how that affects their fate, especially the tragic ones, in the end.
Dunkirk really needs to be experienced in its purest form, but that also means I'm not sure how it holds up as well after it stops showing in theaters. I agree with all the hyperbole from the initial reviews, but I also think that the later criticisms make sense especially if the person wasn't able to watch Dunkirk in a setting that attempts to envelop them. If someone watches this in a regular theater and the movie feels like just another movie without the standard dramatic hooks, then yeah, it can feel lacking.