You can make some very high level prototypes with Axure. You can make them as simple or as complex adn beautiful as you'd like. Discussing, collaborating, and sharing are made very easy. It is really nice that you can use it for other UX tasks like flowcharts and sitemaps - then you can link them all together.

I like that there are a lot of features and that you can manipulate objects/tools by applying programming concepts.

The ability to prototype dynamic interactions and conditional logic. It's critical to be able to do this to really demonstrate the flow of an interface.