I've been working recently in both Adobe Lightroom along with Camera Bit's Photo Mechanic Plus. Working in PhotoMechanic has shown me a few places that Lightroom is really lagging behind and could use a push to catch up!
One weakness I'd like to see addressed is the customization of the "Expanded Cells" in Grid View. My chief complaint is that Expanded Cells are not very spatially optimized. While in Compact Cells the two metadata extras you chose to include show up tight against the image. When you switch to Compact Cells all the metadata moves outside of a massive buffer space, which means that despite doubling the size allocated to each image you barely have any additional space for metadata... if we're going to Expand the Cells lets get some space for more metadata! Otherwise there is no point...
I also really love how customizable the structure is in PhotoMechanic's app. For example, # of megapixels, ISO speed, exposure bias, and many other variables take up very little space – I'd love to be able to show more than two in a row.
I also personally feel that it makes more sense for the metadata to be all underneath the photo rather than on top... but maybe that's just me.
Great product overall and hope it continues to grow and improve with the industry!