Even though HTML emails are made up of the same HTML markup and CSS styles as web pages, they present an entirely different set of design challenges. In this article, Mat Patterson, author of SitePoint's Create Stunning HTML Email That Just Works, explains the email design environment and gives you practical advice to make your next email campaign a success.
I think that this is a great advertisement for an app. It has lots of color, making the reader want to look at it, it has enough information, but not so much that the reader won't bother to read it. It gets the point across through bright colors, a simplified, condensed amount of information, and appealing illustrations.