Gmail's Simple Html Mode is much better than standard mode
mail.google.com
mail.google.com
The new interface worked reasonably well for me on my work PC, but not on my home PC (which is admittedly out of date). Clicking a new message would cause the "Loading..." label to pop up and never go away. The message wouldn't load unless I did a full Ctrl+F5 reload of the page.
I missed some of the automatic categorization of messages in the new interface, but now think seeing things is one big list is clearer. And labels still work to see subsets.
The style was not just in GMail but also Calendar, Google News, Reader, and the main search itself. For a while Google hosted the articles for the Associated Press, and I looked for them among the versions of each story in Google News. The width of the text column seemed to me precisely right. The image carousel, when included, was easy to use and lightweight compared to the monstrosities in other news sites.
I always ascribed it to Google's data-driven design decisions. In 2009 a well-known graphic designer quit Google shortly after starting, because Google made him user-test every tweak. "Yes, it's true that a team at Google couldn't decide between two blues, so they're testing 41 shades between each blue to see which one performs better." (https://www.cnet.com/news/google-designer-leaves-blaming-dat...)
But I also think a lot of credit goes to Kevin Fox, Senior User Experience Design Lead, 2003-8 (https://www.linkedin.com/in/person/). He recently tweeted a article showcasing several Google products at their inception (https://twitter.com/kfury/status/1045169856998305792) though the subheading is, "Google didn’t always get design. In fact, the earliest versions of some of its top products were downright homely." I couldn't disagree more.
I'm unsure how credit should be distributed. Paul Buchheit is GMail's "creator" (He's also a partner at YCombinator). A history of GMail is in Time magazine, http://time.com/43263/gmail-10th-anniversary/. He left Google in 2006 to form Friendfeed, which bears a strong resemblance to Google's products (http://thomashawk.com/2009/04/friendfeed-is-for-winners-frie...). Other former Google employees cofounded Friendfeed: Bret Taylor, Jim Norris, and Sanjeev Singh. But they also hired Kevin Fox.
Regardless, in the early 2000s I loved Google and all its user interfaces. Around 2010 it began changing, and I've liked the changes less and less.