The yellow 997 is certanly still attractive, but in person the 991 is quite different and IMHO more sleek, modern and stylish.  The 991 rear is noticeably more convex (rounded), and the accent strip from the fenders around the spoiler complements that curvature nicely.  The smaller taillights and larger spoiler, along with the wider exhaust panel opening, gives the 991 a flatter and more powerful appearance.  Also, if I am remembering the new specs corrently, the 991 has a lower stance and roofline, further emphasizing the sleeker and more aggressive look.  My opinons, of course...