I used this to review what I had taught and students loved it.
It was frustrating because the students felt that it was new and excitng, especially HTML when I had already taught these skills in class.
They really loved the badges.
They did get frustrated quickly and didn't want to go into the forums to get help when they couldn't solve an exercise. Many of them, especially learners of other languages would sit at the screen and stare at it until I bailed them out.
How I Use It
I used it for an end of the year review, and to give my more advanced students more things to learn. Some of them went out to learn Python.
This year I am letting my Games Design class use it from the beginning of the school year. However, I'm not bailing them out like I did last year.