Photos stripped great features from iPhoto.
With the migration from iPhoto to Photos, I have lost pictures, found many duplicate pictures, lost ALL facial tags, lost the date information (causing photos to turn up in the wrong year/month), and lost the ability to tag the location to photos I take with my DSLR. I am thoroughly disappointed with this app, and more so with how Apple has caused the loss of many photos with the transition.
Apple, you really dropped the ball with this change...
iMac (27-inch Mid 2011), OS X Yosemite (10.10.4)