I am the only one to have Mastered so many Catogories and still not really confident about what I have learned.Some lessons are SO confusing and contradictive,I have learnt a lot (I think),but I am still a bit scared of saying,I AM LEARNING German,I really hope I am not alone?
I think Duolingo is mainly for learning how to read a foreign language which is very useful in itself. It's not very good at teaching you how to express things in a foreign language (for example, you can't find tasks in Translations to translate things from your language to the foreing language). In order to learn to that you have to visit other sites too, forums, german news sites, etc. You can't really learn German well by using Duolingo only. Duolingo is great for getting a grasp of the basics, but it needs to be complemented with other sites.
I'm using Duolingo mostly for practice, but I generally agree that this should be used in conjunction with other programs. Langmaster is decent (though it drives me crazy that I can't use it on Linux) but also suffers the same major limitation - using the language. Immersion through reading and watching and listening to books, movies, music, etc is extremely helpful. However, all of this needs to be supplemented with some method of using the language, writing and speaking. Being able to form sentences spontaneously, recall words easily and employ grammar correctly in one's own compositions is the most important part of learning a language. It's hard to get that here. I take some of the grammar from other learning sites (I'm actually learning Italian, which they don't have here yet) and give myself written composition assignments. It's not quite as good as conversation, but it helps. So, for example, give yourself a task to describe your family or your eating habits. Of course, doing it on your own, you wouldn't be able to evaluate very well. It might be helpful for duolingo to develop some fora for these kind of practice activities so that people can do activities together and evaluate each other.