People complain about 1) lack of joystick, 2) touchscreen and 3) SD card as "worse" (but honestly not to me). What are the others?
6D has 1/4000 max shutter speed and 1/180 sec max flash sync, 5D2 is better in both areas.
6D build quality is also not as good as 5D2, being more plasticky.
6D has 97% viewfinder coverage, 5D2 has 98%.
Considering all of these things, the 6D is not even better than the 5D2 in some important areas. Compared to the D600 (which costs exactly the same), the 6D stands no chance.
And let's not forget that the D600 will be shipping to those who preordered soon, whereas the 6D is not going to be available for some amount of time.