Channel 4 UK does awesome things and one of the things that they occasionally do is fund an educational game. They're usually browser-based games or quick downloadable games like the sex-ed game Privates.
They have a recent game, The End, which is a game about life and philosophy and big questions. The concept is interesting, but the platforming is so dodgy that I didn't get very far in to it the first time I played. I was pleasantly surprised today to boot the game up again, and discover that, even though I didn't make an account, a tracking cookie had stored all my information in a usable fashion and I could continue playing where I left off.
I'm mentioning this to contrast my short experience with Caduceus, a learning game out of Children's Hospital, Boston, that talks about disease. I was immediately taken in by the graphics, the steampunk-style design, and the voiceovers. The game offers me a chance to log in, or just play. Like I always do, I choose the option to just play. I watch several cut-scenes, and complete a more-difficult-than-average matching exercise. Then the game tells me "click here to sign up," and doesn't seem to give me an option to go any further unless I do this. I tried starting over, only to discover that the cut-scenes in the beginning are unskippable, and, no, I do have to sign up after the first activity. I really can't get very far in the game without making an account.
Baby, I'm just not sure I'm ready for that level of commitment.
You are shedding users with this methodology. Trust me. I wish I could find the article that listed the numbers; it's out there somewhere in the list of things I've read about web usability, but searching the internet for things like "increased customers" and "user retention" is just folly.
I have more than a passing interest in games like this, having worked on educational stuff, so I know the reason that this is done is probably because they want to track user behavior and prove people are playing the game. But I also know that an educational game is pretty down low on the list of priorities for most people to actually play, even people who generally look at this sort of thing. So if this is the kind of thing you want to design, you've got to do whatever it takes to keep the friction low, even if that means a nice unobtrusive tracking cookie.