First of all it’s a online application i.e access to and add your email address, password to access different apps by Google. The improvements in the Gmail app is the sharpness of the interface making it capable for a Retina Display. Below is the comparison

Old Version

New Version

Pull to refresh will of course bring up your new email rather than reloading/refreshing the page. The graphics are really cool for your eyes, feels very lite while using.