Well, I've been using the original large controller since 2002. Admitadely, my second one has just started to die on me (right controller won't turn left, and the cable is starting to wear), but having spent time on this small cheap looking effort....I'd prefer to play halo etc, albeit with a slow left turn, with the original.
I have large hands,but that's not the real source of my gripe. What I really can't stand about this controller is the small joysticks, which have an 'all or nothing' sensitivity about them. With the original, you have far greater control over your inputs. From precise movements looking through a snipers scope on battlefield 2, to having a smooth and laser like ability to follow a target in your crosshairs in halo games and brothers in arms.
With this controller it's practically impossible to make precise movements in the heat of a game. Plus the overall construction looks far more flimsy.
The final kick in the teeth is the weak vibration motors that lack the instantaneous and intense vibrations of the original. The only improvements I can think of are the lower profile buttons, but that's only a benefit on the main 4, as the black and white buttons are poorly placed and hard to locate due to their low profile whilst mid play.
This controller is only suitable for small handed gamers who have an imprecise gameplaying style. For the gamer who likes to be able to play with finesse, and become more integrated with your xbox, try and get an original.