The Spotify Team updated the Spotify Free app with a brand new design. I find this new design much better than the current one, and I was mildly disappointed when I upgraded my account and saw the "old" design again.
This new one is much simpler and and sexier than the Premium design.
You can also read this article to learn more about this update:
Updated on 2019-06-21
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The menu design on Premium has recently had a big update! You can check out more details about the changes here.