I just read your question again and wanted to add another answer as it is very different to my original.
I started using the framework because I was impressed with the lack of ViewState and a page life cycle that had to reconstruct all the controls again just to get values.
I was also impressed with it's speed and extensibility.
I love that I can overload everything and add my own flavour to it. I love that I can write Views with no code behind.
I love that there is a very clear seperation of concerns and that it's very easy to maintain.
I like that's it's easy to write the code, get it working and then worry about the view. I hate webforms where everything just seems tied together with no clear deliniation of concerns.