David Pierce, writing for Wired:
Every solid gray icon is now a lighter outline drawing. Headers now appear in bold, to help you navigate more easily. The home icon is still a birdhouse, but it lost the perch—you'll see just one hole instead of two. A little less bird-y, perhaps? Round avatars help distinguish users from tweets. Retweet and Like counters update in real time, letting you watch tweets go viral. And the reply button gave way to a speech bubble that Twitter hopes is clearer in its purpose.
Despite the changes, Twitter still feels like Twitter. And more than any one change, the redesign makes a statement about the platform: The look of the tweet button isn't what makes Twitter, well, Twitter. Neither is the shape of the avatars, the shading of the icons, or even the character count. What makes Twitter is @realdonaldtrump, @dog_rates, and each of the other 328 million or so monthly users who log on each day to answer the platform's perennial question: What's Happening?
I spend more time on Twitter than all of the other social media platforms I use combined. There's no app that relies more on a stripped back design that gets users to the content they want ASAP. When I open up Twitter on my desktop or phone I want to see a live feed that is not filled with extraneous adds, or Tweets from days ago.
Twitter is for life in the moment, it's not an archive.