Duolingo formerly had conversational language lessons, which were 100% audio (not even able to see text on screen). These were phenomenal for actually learning to speak <language>, compared to the generated garbage in the lessons.

Duolingo formerly had lessons that explain new concepts, like a particular verb tense. It doesn't seem to have any of them once changing over the to completely linear lesson tree.

I believe that Duolingo has fallen into a logical trap. They can easily track app engagement. It is known that regular practice is the key to learning a language, but they incorrectly forget the quality of the interactions. I've got my Duolingo 800 day streak still kicking, but I've learned almost nothing with the changes over the last year or so. I'm not terribly sure why I even use the app anymore, as there are plenty of anki decks with the same quality content. (The only thing I'd lose is the speech recognition, but that's so laughably bad that it reinforces incorrect pronunciation.)