I had a lot of fun with this one! I would agree though, however, that there is a lack of content in the main game. I think more kingdom and princess's would be excellent, polishing up menus would be nice, and better descriptions for what things do in game (for instance, i had no idea what the wolves did until after I'd beaten the main game and read the description.) I would say that also adding more dragon levels would be cool and add to the feeling of progression. You could possibly have branching paths for what the dragon could become, with different abilities. Overall, it was pretty good start that has lots of potential, with solid art (especially the dragon and the princesses) and a nice feeling of progression!
EDIT: So after reading some other reviews I learned there was a survival mode, which feels much more developed than the main game. Its a shame, seeing as its icon is so small on the main menu its easy to miss and after beating the main game I don't really see a way to access the main menu without refreshing the browser. Using the main campaign as a sort of tutorial and then launching into the survival mode would be a great way of handling things but as it is now there isn't a a very smooth transition, and I'm sure a lot of players missed survival entirely. A real shame, seeing as the frantic pace and increased options makes survival a much more fun experience than the main game.