A preview of Gmail’s new look
Gmail blog
Over the years, adding countless features to Gmail has made it an increasingly powerful communication hub, but along the way the interface has also become more cluttered and complex. That’s one of the reasons we’re embarking on a series of interface updates to help strip out unnecessary clutter and make Gmail as beautiful as it is powerful. This is part of a Google-wide effort to bring you an experience that’s more focused, elastic, and effortless across all of our products.
I must say I love the new design, I am really happy Google is finally spending time and effort to make their products beautiful!
You can preview the themes today by going to Gmail Settings -> Themes, the themes are “Preview” and “Preview”(Dense).
update: Edited quote.
Source: gmailblog.blogspot.com

