drag and drop features and ability to make wireframes simply and easily

The ability to show different use cases/states in the same format as the desired delivery platform is awesome.

Our product requires quite complex prototyping, as it is too time consuming to iterate the actual product in many cases. Axure provides a huge array of technical features that allows us to create those complex prototypes. By which I mean very particular functionality - the tools are flexible enough to create almost any behaviour, just by the fact that you can replicate programming logic (but you don't need to be a programmer!) It's easy to achieve desired layouts and interactivity, you can nearly always replicate the intended design (even visually, if you need a realistic prototype rather than a wireframe). Axure's sharing service is also incredibly useful; we use this to share among the team and to customers for testing.