Even though it seems to have a bit different purpose as it offers more structured learning, I find Tiny Cards to be significantly more enjoyable to use than the main Duolingo app. The gamification does play some role in that, but I think it's mainly how the learning is organized.
I found TinyCards to be good for some things, like drilling on kana, but I find that the extra context provided with full sentences and different types of exercises in Duolingo to be better long term. But maybe I haven't found the right card decks in TinyCards yet.
