This is a neat idea, but these game captchas have some high level of similarity with in-banner-games (at least to me). Not sure if theses "catch the monkey" banners are still around but they were extremely annoying. I hope you are doing some testing to make absolutely sure that this great idea is not mistakenly experienced as some form of banner ad.
Thanks. We certainly don't want to become the equivalent of 'catch the monkey' We constantly do UX testing. Early on it was an issue that people thought we were just and ad on the page, but we updated our start screen and design. By default, we also show our games in a modal window after people click submit, so they know they have to do it. With these two things we saw registrations increase by 40% over recaptcha.
We're also getting ready to roll out an update to our API that will allow you to hide/disable the submit button until the game is played. Our testing showed this helped increase submission rates even more.
Finally, we are also trying different styles of games to see what people respond to best.
