When researching great apps in the App Store, I try and look for them to meet at least two criteria. First, the app has to have some real functionality to me, and not just take up space on the phone or tablet's internal drive. Secondly, I look for great design. If an app passes the first test and it's something I use on a daily basis, having it look good is icing on the cake.
With Thomas Grapperon's Chord! he covers both bases.