This is an excellent way to supplement learning a language. The format is intuitive and really fun and rewarding.
I am currently using it to study German, a language I knew almost nothing about before I started, and I certainly feel like I make progress every time I use the app.
Some small complaints: New words and tenses are sometimes given without an explanation or definition (though sometimes you can click on it for a definition).
Capitalization in the word selection games usually gives away the first word.
I like that the app keeps it super simple-- just turn it on and play the games. But a short little introductory paragraph to each section would be nice. For instance, describing why certain tenses are used in certain situations, and which new words will be introduced.
I really like the audio analysis questions. Pretty impressive that that is even possible. I wonder if some analysis for where you went wrong would be possible.
boldstandard about Duolingo Learn Many Languages for Free, v5.0.14