When Google made the move to Inbox, I switched because I wanted to be using their newest interface. Over time I came to absolutely hate it and that drove me away from Gmail.
My wife still uses it so I occasionally find myself in the Inbox app on our tablet. Just a few days ago, actually, I read something in her inbox and for the life of me I could not figure out to mark it as unread from the inbox list. Maybe I was just missing something obvious, but it was very frustrating to not have such a simple action easily available.