Initial thoughts (duolingo on Acer C720): a lot of the UI design is pretty unintuitive, and although I'm sure I'd get used to using it with a non touchscreen and a physical keyboard, it just feels suboptimal. Also a weird feeling having Android-like prompts on a 'regular' computer. No fullscreen, so I'm left with a small window on an already small (11") screen. Functionality-wise, does what it should, but I'd much much rather have an offline proper chrome app. Currently, it'd be my last choice behind my android phone, iphone, ipad, and laptops I have with me right now (I realise I'm unlikely target audience).
This is exactly my experience with Evernote. Although I've used it on the C720P with the touchscreen and it was a bit better. But the fonts look really small and the fact that you can't make it full screen is annoying.
But it is still better than the Evernote web app. Now the question is: given all this, is Evernote (and Duolingo, etc.) motivated to release a proper Chrome app or not anymore? My fear is that they are not, which is bad from Chromebooks.
I'm fairly certain that, at least when I was using it a year or so ago, the Duolingo website was better than the Android app. So it's odd that they chose this as one of the first apps to port.