The effects and the interface...simple interface like a ppt and simple enf to use...yet powerful enf for advance users

Interactions are assigned to objects -- so you create one page and then can change things dynamically on the page with different views, etc. A lot of prototyping tools just click you to another screen but Axure has hover states, scroll commands, dynamic panels, window resize changes, variables carried across screens to keep context and a million more ways to control interactions

It is easy to use with great short video tutorials if you get stuck. You can get a design or even a working prototype together in minutes to get feedback and write requirements.