I don't see how anyone could call Photos.app the best app they've ever used. Right off the bat, I can never tell you why I'm in a mode where I can multi-select or not. When I double-click on a photo, all of a sudden an intermediate navigation thumbnail bar thing pops up, but it doesn't let me do the things the main thumbnail view does.
I don't know when I can use the back arrow or not.
Flagging no longer shows up on the pictures, so I have to look up to the menu bar to see if a photo is flagged.
I've got a few shared galleries with family. Does anyone know which photos are going to show up in Photos vs Albums (All Photos) vs Shared (Activity and your named shared galleries) and the My Photo Stream under Albums?
Virtually every time I recreate a photo library or get a new device, I need to turn off all the icloud syncing crap and photostream crap about 3 times before it finally starts syncing photos. And sometimes when it does, I click on a photo thumbnail and the wrong photo pops up.
Photos is effing TERRIBLE from a UI/UX, features, and functionality standpoint.