What does richer user experiences mean? “Richer” in this context has two distinct meanings. The first one means a better-designed, more intuitive, and more user-friendly graphical user interface. The other means a cleaner interface, one that is not excessively crowded with options and links.
The main advantages of AJAX include e.g. short page download times, smooth and interactive user interfaces which increase user satisfaction, a user interface that is always on view, transparent data transfer e.g. in the form of showing download progress, new kinds of interaction methods, and convenience-increasing functions such as predictive text input in text fields.
But there is one drawback. Pages dynamically created using successive AJAX requests do not automatically register themselves with the browser’s history engine, so clicking the browser’s “back” button may not return the browser to an earlier state of the Ajax-enabled page, but may instead return to the last full page visited before it.
Therefore Rich user interface features seem to improve the user experience by making the operations easier and faster to perform as shown above.