For a demo it was fun
I'll be fair and score it based on the game, not because you'ld have to pay $20 for the full version. I in fact like it quite well, if you read the what your supposed to do in the mission there should be few problems. The one thing that could have been better is the music. But hey, you work with what you got. The demo, contrary to what some belive, is in truth the perfect length. It gives you a taste of the game enough to like it, while keeping it short enough for you to want the full game.
I do have to agree that 20 dollars is high for a flash game though. I would buy the full version save for two problems:
1. Don't have the money.
2. It's also a bit pricey. I would pay $10-$15 for it, but no more. It is something you can sell.
One thin I suggest, open up the free battle, with limitations. It'll give consumers a better taste of the game without having to go through the full demo.
Over all, 9/10 and 4/5