Because the whole screen is now a drag area, it's also much more prone to unlocking by accident, either in a pocket, or simply when picking it up. - Binary Bonsai
The new lock screen is a strange one. I find the camera icon unneccessary, with a swipe-up you can easily reach it in the control panel too.
And the removal of the slider resulted in an iPhone that unlocked in my pocket, started typing in a multiple of wrong passcodes and me being locked out of my own phone for half an hour..
So, it's a nice redesign, but Michael's right, there are some issues.