If you found the original Xbox controller bulky then there can be no doubt that Microsoft have solved that problem. This new design is sleek, asthetically pleasing and very comfortable. The fact that the white and black buttons have been changed to bumper buttons near the triggers is also a nice change.
The batteries included with the console have lasted a long time and the wireless aspect is perfect. The Xbox guide button is also a lazy man's dream as you can use it to turn the console on and off, as well as access your Xbox live account and hard drive saves through an accessible and intuitive interface. As long as the game your playing is in the console why go through the trouble of getting up to play your console?
The short of it is; this controller may well be the best first party effort I've used. Which is saying something, because I personally really liked the Gamecube controller as well. The only downside is, as with all wireless things, the batteries will die on you sooner or later but the energizer batteries seem to last really well and at the end of the day, the wireless freedom and sound design more than makes battery swapping worthwhile.