While Windows Phone 8 does work well with Gmail, I get the feeling that it still works on the IMAP model. MetroMail is a third-party client that provides a more Gmail focused inbox for WP users:
While Windows Phone’s email application does handle Gmail in a way that fits in with the UI, there are some areas where it can be lacking (including label support, filtering, and multiple accounts). Does the third-party client MetroMail address these issues and, if so, is it worth Googlers switching to it? That’s a finely balanced decision.
My full review is over on All About Windows Phone.