The only thing I dislike is that the icons on the top seem too thin. I wish they were as thick as the arrow near the "Mailboxes" label. This is nothing against you though, it's just what I dislike about iOS 7's new design... but other than that, this is a really great concept! I would love using something like this. Very simple indeed.
This is so amazing and professional! It really is the design from iOS 7, and you made it suit OS X. I think the current aluminium look of OS X is beginning to look old, dull and boring, just like it did with iOS 6. I bet this is direction OS X is going to go. I love how the bar is transparent and displays the content of the mail. So beautiful! I think you should do some more examples with some other apps (Safari, Finder etc.) and send it to Apple. Like really, send it to John Ive. But remember to add a fullscreen mode icon.
Thank you, I was going to uploaded a few more instances of this then start other applications. The full screen icon's ghostliness was a mistake; subconsciously due the the hours it took when designing an Elementary full screen icon to be pixel perfect.