When you login to Gmail today, you may find the a small button below to switch to the new look. I think it’s awesome, now Gmail offers 3 layout to cater different screen sizes and perhaps the looks that pleased your eyes. No worries, you can try it first and if you don’t like it can switch back to the old layout. However, this revert back option would eventually goes away when most users already switched to new look. So you better get familiar with the improved layout. Some of the best improvements are easier vertical scrolling for both email lists and labels at the left side, with Gmail chat hidden when you want to scroll within the labels. Great for users with lots, LOTS of emails and use labels everywhere in Gmail.
You should try it now. Check your Gmail.