HTML5 Gaming

Is it possible to write games in HTML5 now?
whats going with opengl es and webgl?

I've already written a game in HTML, so of course you could.  It was an adventure game, like Zork, but with pictures on each page.  You typed your actions into the URL, so after playing for a while you would be on a page like this:

http://www.game.com/go.left/look.tree/get.branch/hit.nest.html