I'm really happy with my M.
Bodies: 6D, 7D, EOS-M, S100
I'm curious - since getting the EOS M, how much do you find yourself using your S100?
My S95 usage has decreased dramatically after acquiring an M.
(...just wish the M didn't require an external flash.)
Size matters. The M, with any of the M lenses, is remarkably tiny...and with the 22mm pancake...does work in my pocket for a couple of hours while touristing.
The S series, of course, is even more pocketable...and the ELPH 300 is even smaller than the S series.
I think carefully about kit size and weight while on vacation and out-and-about with family; the M fits VERY nicely in the mix.
When the sensor science enables DSLR-quality autofocus, mirrorless, I think, will replace APS-C. That's right. I said replace.
I am terribly impressed with the M because I still think about it like a large sensor point-and-shoot. If I thought about it as if it was a DSLR, I would be disappointed. When the sensor improves enabling better autofocus, etc, I really think the sky is the limit.
I still enjoy using DSLRs...but using the M (and, for that matter, the S95) is fun!