I find the iPhone 6 Plus to be large compared to my iPhone 5, but I quickly became accustomed to the bigger size. When I see my iPhone 5 now, it looks like a miniature to me instead of the iPhone 6 Plus looking like a giant. I think the slim form-factor helps with that perception.
Big; beautiful; clear screen; Widescreen format for watching movies; Bigger format may allow this phone to function as a tablet replacement for some; Thumbprint reader works very well; Camera takes great still photos and image-stabilized; slo-mo; and time-lapse video; Allows landscape orientation...
May be too big for some people's taste; Power button has been moved to the side; Will be too big to carry in some people's pockets