Google has redesigned Gmail, which was launched in the year 2004 and remained in beta version till 2009. The new redesign is not the only thing Google is embarking on, rather it's a series of interface updates to help strip out unnecessary clutter and make Gmail as beautiful as it is powerful.
What's New ?
As per Google Blog -
To start things off, Gmail has two new themes for you to try out as a sort of sneak peek. There is a "Preview” and “Preview (Dense)” themes in the Themes tab in Gmail Settings. The idea of two themes is to accommodate different screen sizes and user preferences, but until then you can pick the information density that you prefer.
Here’s what one of the new themes currently looks like:
And in conversation view: