For me, Carlos just has an incredible understanding of human form and the way it works. I'm not talking so much about simple proportion, more the way figures stand, how their weight distributes and the way they move in his work all seems very natural and dynamic. Even a fairly static, front on piece of two figures walking above has a sense of natural movement and the figures have poise and presence that can be hard to achieve and comes about through underpinning knowledge and talent.
I love John Burns' stuff- he's a great artist, vastly experienced and great with figure work, he's another one of my 2000ad favourites. But even he has the occasional stiff, awkward looking poses where it doesn't quite work.
Carlos' work just never gets old for me, I love his trademark 'untidiness', he's been my absolute favourite comic artist, since I first clapped eyes on Portrait of a Mutant. I love a lot of artists work a lot and for many varied and sometimes conflicting reasons; but I just love his more.