I saw the Lange exhibit at MOPA as well, and felt the same way about her images. There were some standouts, but many of the prints didn't catch my interest. I felt like there were too many prints exhibited in this show and towards the end I just wanted to get through it all.
I usually like to take my time when looking at exhibits (especially traditional prints) and don't like to "skim" over them. I want to be able to appreciate the details and nuances of a good photograph, but was finding that some of these just weren't very interesting. It may have been better if they had selected the strongest images and displayed fewer prints for this exhibit.
Conversely, the Arnold Newman exhibit showing now at the San Diego Museum of Art is awesome! There are also a large number of prints in this exhibit, but it was a very interesting take on his career and the subjects he photographed. There were many photos I had never seen before and I would highly recommend it to anyone who has a chance to see it.