how do i play all songs in a genre

I Completely understand your frustration bc that is how I listen to music 98% of the time. I was about to take my iPhone 6s back to the store, despite the fact that I am familiar with Apple/Mac hw & sw, as an owner of a 1st gen iPad and a now older-ish Mac computer. BUT I HAVE AN ANSWER, much to my own relief and, happily, it doesn't mean using an extra app. When you are on the start screen of the music player, under the album art which is at the top, are some magenta letters that may say "artist", "album", "composer", etc. Touch the drop down arrow and select "genre" then simply touch the ICON to the left of the genre you want and a song should start to play. Once that happens, gesture up on the narrow band at the bottom that is now showing your play arrow and the curecently playing song. On the screen that opens, make sure that shuffle is boxed in gray. Voila, the player should now shuffle songs from the selected genre.

Two options:

(1) Instruct Siri to "shuffle play Blues". Sometimes she will understand perfectly what you wish, sometimes (especially if you have an artist called Blues) not so much.

(2) I created smart playlists for each of the Genres that I use (Blues, Rock, Jazz, Live, etc.) I can then select that playlist and playlists all had the Shuffle option returned with iOS 9. Nice that they did that for playlists, artists and all songs - don't understand why they did not do it for Genres yet.

THank you, it worked just as described. Yeah!