No the home page doesn't validate
The second page I checked "HTML Tutorial" from the drop down menu didn't validate either.
The homepage had 6 errors and 3 warnings. The HTML tutorial page had 5 warnings and 15 errors
I would give the site an 8. The site is clean and well organized. It lacks polish in my opinion though. The the huge multi-color bands of muted pastel colors that seperate the different languages on the site look less than professional.
I would give the site a 9 for usability. Navigation of the site is easy. There is a clearly defined navigation bar at the top of the page that really makes scrolling unnescessary. However if you're like me and you have to scroll there are sample windows that let you play with code and see results immediately which are really engaging. There is a deep well of reference material that you can jump into right from the navigation panel, but I would be careful jumping in because you could have trouble getting back out.
?Assuming the purpose of the site is to boost interest in coding and to provide resources to facilitate learing of code I would say that it meets it's purpose.