At a high level Edge will be like a Flash-like program that will output HTML5 but it gets a little tricky when you get into the specifics. This is because HTML5 as a technology platform is still changing so it makes developing a tool that uses that platform much more difficult. Adobe is trying to address that by releasing the software into previews much earlier than normal but it will mean that there may be significant changes and additions to the program before it releases a final release state. This is also why you will see that the preview version only currently does animation but Adobe has said that this will be shortly followed by shapes, expressivity and coding, and then interactivity and graphics will arrive for testing in the public pre-beta before an expected final release of the product in 2012.
Since Adobe let Apple dominate the Flash vs. HTML debate we all knew a move like this was coming. We will all just have to wait and see how powerful this tool can become to truly be something we can use as an HTML5 replacement for Flash.