I spent fifteen to twenty minutes reviewing the games on the site. I found the site easy to use and a great way to understand concepts in another method of presenting the material (game).
Im not a games person, so I would not go to the site for "fun". As a classroom tool, it may provide an alternative method of expressing more difficult concepts and ideas and a more user-friendly fashion.
The site was easy to use, understand, and not difficult to navigate. A quick browse enables the student to see what is available very quickly.