Exactly my experience with Duolingo too! Love this application and am hooked to it.
Having said that, there are still some things i would do differently: if you stop using the app for few months, it’s pretty dull to start again. At least for me it was. So i wouldn’t make the user to start from the basics. I know you can practise the difficult stuff as well if you’ve been advanced in some point, but you can’t really move forward before you’ve done all the beginner’s stuff as well. This stopped me from getting hooked to it again for some time: I needed a very dull moment to go through all the basics in my French in order to make some progress again. But now I am in a roll!