I could be wrong, but I think Nintendo has been very hands-off when it comes to old Mario stuff. It's blatantly infringing, but they probably won't even send you a C&D.

It suffers by not fully committing to the idea. For example, once I've gone into a specific event category, now I have to use my mouse to navigate and scroll. Oh well. It's a nice HTML5 novelty, but just as unusable as all those terrible Flash sites.