Xamarin.Forms is a crazy productive framework for build cross platform apps. However, straight out of the box you might find your User Interfaces a bit bland. A good understanding of the layout system (and a good graphic designer) are really going to help you make your UI's awesome. (or at least not suck)
In this repo, I'm going to recreate some nice looking UI's that I find around the web (places like Dribbble) with Xamarin.Forms.