I think the old ones look old, ugly and unpolished. They creak and bend when you pick them up. The keys look messy and get dirty. The gray-beige plastic joints are messy, unsightly and ruin the look of the aluminum. The fuzzy material guarding the CD-ROM slot is not well-protected and gets scuzzed up after a while.
The new ones look amazing - crisp, clean, neat, precise. They feel like a solid block of aluminum when you pick them up. They're thinner.
They're the best-looking laptop ever made. The old laptops are the ones that look like HP knockoffs at this point. They're still the second-best-looking laptop available, but there's a large gap to the #1 spot.
Apple has a unique talent for releasing a new model that immediately makes the old one look like crap.