I have a M and it's bloody marvellous ! With the 22mm pancake, it's light for hill walking, pictures from it are great, it looks like a cheap compact to a hit and run thief... And importantly, gets the important capture of your life when the FF + f2.8 is just too heavy or big or expensive looking to carry along.
If you don't like the M, fine, manhandle your DSLR ;-)