Absolutely fantastic! BUT...
Great, very well made, you can see how it went into much thought. My only request is: expanding the number of languages. Out the boundaries of Romance languages. Maybe Arabic (Classical Arabic, Arabic itself has a lot of dialects) or Korean / Mandarin or even - learn Latin! Meanwhile, I have only good words on the interface, design, and implementation. Duolingo is wonderful.
Woohoo! Giggles.... "weeks" I just noticed you said "weeks". Everything else I'd heard was in the distant, nebulous future. Wow. now, I have something to look forward to. I know I shouldn't get too excited because this might just mean we will get an announcement stating new languages will be added in the upcoming year or so, but this is almost a firm date. AWESOME NEWS.