Definitely one of my favourites. It was partly down to the excellent, paint-based colouring too, but I remember being absolutely enthralled by some of the visuals of Year One. There was just something really quite simplistic about his cover design, too, but it was all composed really quite perfectly and it looked wonderful. The trade designs for various versions have looked beautiful, too, and shows that he isn't afraid to dabble a little in other materials. The Deluxe Edition of Year One in particular has one of my favourite images of Batman on it - Doing the traditional 'cape over face' pose, but with the arrangement of the dustcover at a sharp, parallel angle to Batman's arm, it just works beautifully.
Superb artist, and definitely someone I'd rank up along with Kirby, Eisner, Perez, and a couple of the newer artists such as JH Williams III, all of whom have or had some standout element that made their particular work fantastic, be it Williams III and Eisner's sense of design, the ability to handle a crowd scene like Perez, and so on.