Duolingo doesn't quite reach the necessary levels of engagement and nuance to be able to fully learn a language. It is best used as a companion app for more substantial resources of your target language. The biggest drawback on the mobile app is the lack of "tips" with each new component. Duolingo's main pull is the mobile gaming aesthetic and pseduo-competitive method of teaching the language. It looks nice, sounds nice, user friendly but is ultimately a farce.