I like the idea of the puzzle pieces having three stages, instead of the normal two. The fact that there’s going to be kongregate API is also a plus! A few things to add: definitely have more levels, some music and sound effects, deeper backgrounds. Also, I would add a timer, and of course kongregate API for reporting how long it took to finish a level. And maybe if you are good at actionscript add a random level generator!
You may want to post this in the Games forum, and ask for feedback on parts you aren’t sure about in the future though!