I would have to rate this one "difficult" for a number of reasons. The multiple layers of adhesive requiring some pretty tough spudgering, the many tiny zif connectors, and several antenna cables (with an even greater number of antenna cable sockets!)
On my M8, the upper end of the long black antenna cable was underneath a black plastic shield, and unfortunately this cable popped off this socket, which took a fair amount of effort to put it back in place. I also had to remove two additional antenna cables on the left side near the top (one short white, another even shorter black) that weren't mentioned in this take-apart in order to remove the motherboard. Since there were several extra antenna cable sockets in this area (and elsewhere), I would recommend taking a picture of your M8 motherboard (at about step 10, above) to refer to during reassembly so you don't use the wrong antenna cable sockets when you reattach these.
Took me a good hour.