Impressions:
- Your website and your app looks neat, although I'm not a fan of "children colorbook" style.
- I like that you can vary difficulty level without having to "unlock" longer sentences.
- I hate that writting has to be perfect to the punctuation, esp since I do not always know how to write some punctuation marks or accent with my english keyboard (I went with learning spanish)
Fundamentally, I do not think it's that very different from duo-lingo though (that's just my first impression of course, but you might find it interresting anyway - maybe put upfront what really differenciate your app?)
Do you know about the "Language Transfer" app, which approach to language learning is also centered on listening (but in their case, listening to conversations with a teacher)?
Best of luck!