The Dualshock 3 replaces the Sixaxis controller that originally shipped with Sony's Playstation 3. While the Sixaxis was a lightweight wireless controller with tilt sensitivity that works well in certain games, it lacked a critical feature that had been an old standby on Playstation consoles since the very early days. This feature was force-feedback, and had been in every Sony controller since the original Dualshock. Sony cited a lawsuit that prevented them from adding force feedback to the Sixaxis, but they seem to have surmounted this obstacle, because rumble is back!
If you've ever used a Playstation Controller, or a Sony Dual Analog, or a Dualshock, or a Dualshock 2, or a Sixaxis, then you'll be familiar with the ergonomics of this controller. The overall shape has changed very little, though with the Sixaxis came the minor changes of making L2 and R2 triggers and adding a PS button to the center of the controller. This replaces the very outdated button to toggle on or off use of the analog sticks.
From the moment you pick up the Dualshock 3 you will notice that it is fairly heavier and more substantial than its Sixaxis bretheren. However, it isn't uncomfortably heavy, and it actually feels like a legitimate controller now. The force feedback is not quite as powerful as the Dualshock 2's, but it's the most powerful you're likely to find in a wireless controller.