I think this would be great to use at home. But I think that it is difficult to keep the students on the math games and not the more arcade type games on the site.
My students love the games provided on this website. I am constantly looking for ways to increase their math accuracy and speed (they are in second grade and really need the extra help to get away from finger counting). After using this website for an extension to one of my math lessons, my students asked me when we were going to have math class...and I said we already had math class when we went to the math games website. They then told me I tricked them into doing math and that wanted to do the same thing tomorrow. So, I love this site as a teaching aid.
Other than guided activities I use this as a fun center for math. Students can go to the website and play games that fit where they are in their math activities. I do wish it was a little less advertisements and a little more easily navigated by younger kids though.