It seems to have trouble doing anything over https (the site loads, but the games don't due to CORS issues). Normally I have the HTTPS Everywhere extension enabled, figured out I needed to disable it to get the games to load.
Very cool, but the experience was ruined when I was testing a game I made and was interrupted by a lightbox saying "Seems like you have done a nice game! If you want to continue making awesome games and saving them, you should register! It only takes 10 seconds." I get the reasoning for this, but I'd suggest a lighter touch for prompting users to sign up -- namely one that doesn't interrupt their gameplay. The lightbox is a great way to turn people away from your product.
I help develop Goo Create so it is really cool to see other people making cool stuff for the web :)