Google have been working on updating and improving Gmail.
You can switch over to the new look by clicking on Switch to the new look link in your account.
Some of the changes that have been made include.
Conversation view has been completely redesigned to help you read through your email threads. You’ll now see profiles pictures for your contacts, so it’s easier to keep track of who said what. Google have also stripped out as much as possible so you can focus on communicating with your friends and colleagues.
Google know that you use Gmail from a variety of screen sizes and devices, so now the spacing between elements on the screen will automatically change based on the kind of display you’re using. If you prefer a denser view all the time, you can change your density manually in the Settings menu.
New HD themes
Themes have been completely rebuilt to enable Google to bring you a new set of beautiful high resolution themes with imagery provided by iStockphoto. Most of the old favorites have been updated as well and your theme will be automatically carried over to the new look. Go to the Settings menu to take another look at themes and choose the one that fits you best.
The navigation panel on the left keeps your labels and chat contacts in view at all times. It's also more customizable: you can resize the labels and chat areas if you want to see more, or hide the chat area entirely via the chat icon in the lower left. You can also use the arrow keys to navigate around the interface.
Click the dropdown in the search box to see a new advanced search panel, which makes it easier and faster to find exactly what you're looking for. You can use the same panel to create a filter from any search in just a few clicks.
This video gives an overview of the main points of Gmail's New Look.