My only issue with Duolingo is that I wish there was somewhere to get much more formal information on the grammatical rules. Their inclusion currently is really poorly executed, haphazardly located in certain lessons as if random. I’d love if I could get specific lessons on demand for anything I am struggling with.
Also, it is really annoying how sometimes it gives you the translation after you are done and other times it just says “Great!” Or something similar, so if you are slightly unsure of something you don’t always get the actual translation to help clarify.