Could you elaborate on which features you'd miss from Duolingo if you switched?

For context I'm working on a language learning app (phrasing.app) and I'm pretty against gamification. I've got a couple different review methods (listening, tapping, and typing) but I assume you're referring to a more complete feature set.

PS: If anyone wants to beta test the application, contact me on twitter @barrelltech. I just got everything re-released this weekend, so I'm just now starting to work on user guides and documentation!