I must admit gamemaker is a superb program, and I recommend it if you are a newbie to making games.
The only downside to it is that your game is published in an .exe file. So if you want other users to play it they have to download it to their computer first, and they can't just play it in the browser. Also, you must use bitmap style sprites for the game, as opposed to the flexibility, scalability and easily animated/modified vector style of flash.
But I would definitely give gamemaker a try as a starting point before you move on to other things.
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