HTML5 is not a coding language. Javascript is the language and HTML is the layout. Googles pacman was made using HTML5 elements (well, really just one element) and javascript.
Now, as to how impressive this is. Pacman is an incredibly simple game. After all, it had to run on 70s era hardware. The fact that it can be done with HTML5 and javascript really isn't something that is impressive. (though, the fact that the googlers put it together is impressive. Working with JS like that is not fun).