I have an aluminum Macbook and sure it's nice... but when I think about Macbooks, I think about that white plastic machine. Shiny, almost see-through. It really stood out to me in a world of dull metal and chunky black plastic and laser-etched designs on laptops. My 2015 looks nice, I guess, but in my mind it doesn't look nearly as nice as that shiny, translucent white Macbook I saw years ago.
Now, I never used one and I'm sure a lot of people here have, and I'm sure there are a lot of negative stories about them cracking or discoloring or being squeaky or something. But I still remember the first time I saw one, and it stuck with me. That was the same when I saw an aluminum Macbook, it was nice. They don't look all that special these days, the design is getting stale. Everyone has a Macbook-looking laptop, from a distance I can't tell the difference between a Samsung Chromebook and an 11" Macbook Air.
I hope they can wow us with a new design again in the future.