What new features are available in AJAX that makes it powerful?

AJAX makes a web page to loaded dynamically. We don't need to refresh page everytime we make a change.

I am not sure on "What new features ?" There might be a lot which depends on your requirement.

As of me, User Experience is the best part of Ajax. It eliminates the "START-SOP START-STOP START-STOP" factor. When you have  huge hit rates over the system, It really matters.

IMHO

Ajax has the following key features which makes it so powerful

1- Asynchronous communication between server n client

2- bosst web app speed due to partial postbacks rather then full post backs to server

3- Efficient use of bandwidth (though the differnece can be small but it does impact when you have bigger userbase)