Remember when Gmail
escaped Beta? Doesn't feel like that long ago, but it definitely took Google a really, really long time to finally cross that milestone. And now, the company's finally giving their Mail application the first major facelift that we can remember. For now, the company's leaving these new themes in the "optional" folder, and they've only pushed a few very minor button changes to the masses. But if you're feeling curious, you can poke around in the options / settings to see what's to come.
It's just a small part of a Google-wide effort to deliver an experience that's "more focused, elastic, and effortless across all of their products." The sneak peek includes Preview and Preview (Dense), which showcases the new interface. Google says the interface will eventually expand dynamically to accommodate different screen sizes and user preferences, but until then you can pick the information density that you prefer.
Google says it's cleaner and more modern, but a lot of avid users are griping that the spaces between emails is now too large. Google admits that a few Labs features act odd in the new themes, but that they'll be working to fix them. So, try 'em out, and see how you prefer (or don't prefer) them. Hopefully Google will allow users to keep the "old" look if they so choose.