I like Duolingo a lot. I don't think it sucks at all. The only problem I've had with the app is that the sentences per lesson are planned by a teacher with clear learning objectives. But, despite this they use speech synthesis for everything but the stories. The synthesized speech is comprehensible but, it seems sort of lazy on the part of the Duolingo team. Especially when so many apps use native speakers for their quizzes.