Strong points: It didn't crash my flash. 1+ star right there. Good job.
The concept is okay, actually. It's a good take on a popular board game.
Flaws: People don't often like to register/give emails to play games. In the future, you should drop that feature and allow people to play direct. While I understand that you wish to create a large-scale multiplayer game, this is not how you should pull it off.
Some units (here's lookin' at you, archers) are overpowered, and can pack on the hurt for a newbie cornered by a more experienced player. Try to even the playing board a bit. Think of a rock-paper-scissors thing instead of unbalanced game-play.
The synching with other players seem to be rather buggy. Sometimes, both players can get stuck in an infinite loop of 'waiting for other player'(noticed this happens a lot in guest mode). You should create a 'play alone' option first, then build on that. That way, you have a stronger foundation for the whole game.
Well, that's that. You seem to have a talent for making games; I hope you learn from your mistakes and continuously improve on your product. Good luck!