Very recently the guys from Gmail submitted its official application for iOS (and is version 2.0) which includes a total remodeling it.
This time the application interface has been completely redesigned so that we have an app fully optimized to maximize the benefits of iOS. In short this is an optimized version of the web application, but as I say modified to get the most from devices equipped with touch screen.
Regarding new features in this new version 2.0 we find several interesting: Support for multiple accounts, infinite scroll (scroll I mean the inbox, allowing us to review any mail inbox no matter how old it is) , autocomplete predictive (a great help in the searches), response to invitations from Google Calendar from the same application, and (of course) better integration with Google+.
Finally it should be noted also optimizing the app in regard to their performance. I mean the emails are received very quickly as the flow of the application is very good.