Overcast is an immensely popular podcast app for iOS with over 12,500 reviews and an aggregate rating of 4.5, plus thumbs-ups from The Verge and others. Marco Arment, who is also the cofounder of Tumblr and creator of Instapaper, documents the process in detail:
I designed Overcast 1.0 in 2014 for iOS 7, and it was a product of its time: it used ultra-thin text and lines against stark, sharp-edged, full-screen white sheets and translucent blur panes, with much of the basic functionality behind hidden gestures. That fundamental design carried through every update until today… I’ve been working on [the update] since last summer, informed by over two years of testing, usage, and customer feedback.
Arment shows the before and after of most of the key screens, along with his reasoning for each of the changes; and it’s worth a read.