I did indeed register for this, and spent some time on it, but I decided after a while it was just too laggy and took hours to load things, so I never did spend long on it. But with my short experience on it, I quiet enjoyed it. I never did get to fly my own dragon, as I didn't stay on long enough for it to grow up, but on the tutorials on how to fly the dragons, I found it very fun :3
I would recommend it to any of those who like How to Train Your Dragon, or those who generally like dragons. It is enjoyable, with plenty to do and discover. Also, mind that you have a strong computer that can handle large games.