With the redesign of the music app in iOS 7, Apple also removed the ability to directly playback an entire track list from a specific genre. While Smart Playlists would still be one obvious workaround for this, this may not be practical if you have a lot of genres and are used to being able to easily select them.
The good news, however, is that you can still workaround this. Swipe downward to reveal the search field and type in your Genre name there. When it appears in the search results you can tap on it to view all of the tracks assigned to that particular genre, grouped by album. Tap on an individual track and your device will begin playback using the displayed list of tracks as your playlist.