1. Space Gray. No black (the black front doesn't count, I'm talking about the metal case).
2. iOS 8. (Give me iOS 6 back please, I'm only on iOS 7 because I replaced my iPhone).
3. Those fugly antenna lines. To each his own, but I do NOT care for that look at all.
4. Non-flush camera. Seriously? The phone is so thin the lens has to bulge out? I've heard rumors that it's to allow for future attachments to the lens, but it's still ugly to me.
5. It's curved. I much prefer the boxy side look of my iPhone 5 and the chamfered edges.
I do however appreciate the size of the 6+. But, honestly that's about it. This is not one phone I wish to spend the next two or more years with.
Now, to be honest, there was one thread where a poster showed a mod that would anodize the phone to a jet black. It's an additional $300 and I do believe it makes the phone look a lot better. Being able to execute on that option as part of getting a 6+ would be a motivator for me to buy a 6+.
Space gray is not black and I much prefer black for my phones.