True, Duolingo might not be the best way to learn a language but it is good as a starting point. Learning a new language is tough and when you are learning alone, its even more challenging. So many people give up on this. Duolingo realised this problem and hence introduced gamification on their app due to which many users are hooked on completing their lessons. They have made the learning fun and competitive. The app may not make you a fluent speaker or writer but it can help you learn the basics.