From an architectural perspective I agree with the OP and find MAD to be very very impressive, but the Madrid airport authorities always had something BAA did not: the luxury of space, and as others have pointed out, that luxury of space equates to very long distances between points A and B in the terminal. But if you're a fan of architectural form (like I am), it's a masterpiece.

I agree that some of the signage in T5 needs to be improved, but given the space available for the terminal and the number of passengers it needs to process, I generally don't think they have done too bad a job and the subsequent and inevitable high-rise element to T5 has been executed fairly well (and looks quite impressive at night when you're stuck outside in a plane waiting for a gate to become available!). That being said, the inevitable surfeit of shops and F+B outlets do give it an air of clutter, particularly in the main Departures concourse.