I just have been here only a couple of weeks, but i'm already a huge fan of Duolingo. What i like best is that you're not flooded over with new difficult words every lesson, but in the beginning the focus is more on getting the basic feeling how that specific language works using very limited vocabulary. I think it's very important. Another thing with Duolingo - it's fun! It's like a game! For me it's even hard to stop with lessons whenever i'm here, i have so much fun i just want to go on and on! Yet there are two things i think would improve over all experience and make learning even easier.
First: would be very helpful if in dictionary you could also see the gender/article of the word right away or when hovering over. Clicking on the word that takes you to another page is a bit bothersome and time taking. It's been pointed out so many times - learn the word with its article (and especially in German it's crucial). I think this would make learning them faster and also put your visual memory to work.
Second: another great thing would be if one could "bookmark" the sentences in the lessons that appear too difficult or confusing at first. This way you could come back to them and practice them over and over until you get it right. So you'd have this very special section on your personal Duolingo page where all these "obstacles" are compiled to and whenever you wish you may easily find them and practice again. And again. At least i would love it! At the moment i'm just writing these sentences out on a piece of paper, because usually the entire lesson goes easily, but from time to time there is one single sentence i'd like to work more on.
Most important thing i want to say though is - Thank you Duolingo Team! This is the best language-learning website! Seriously. Not only that it's free, but it's immensely fun! And it's easy! And you really learn fast, you're not so much stuck to charts and dry rules, but it all comes so playfully and naturally! Just perfect :)
I like both, but I especially like the first one. In German, I'm often wrong because of the article/adjective endings if I'm not familiar with the word or if I don't remember it's gender, and it would be nice if I could check the gender, not only the correct solution for the whole sentence, because some genders have the same endings in certain cases.