Robert A.M. Stern seems to be everywhere these days. Besides running Yale University's architecture school and producing architecture tomes as fat as two-by-fours, he oversees a large and successful architecture factory in New York City that can turn out buildings in any style you need. It has been doing a big business in Philadelphia. His firm's substantial output here includes one of his finest buildings ever, the Comcast Tower, a handsome modern obelisk. He's also responsible for a truly awful one, the McNeil Center for Early American Studies on 34th Street. That dull redbrick box is decked out with plasticky-looking white windows and just enough design cues for it to claim Georgian ancestry. It should be a cautionary tale for those hoping to re-create historic styles on a modern budget, particularly in a city that knows the glory of the real thing firsthand.