First off, the EOS-M is a very capable camera with a great sensor and processor. And IQ wise it matched the DSLR 650D, in actual fact many reviewers noted that the EOS-M is a 650D in a smaller package.
Canon's first mirrorless camera came into a very very fiercely contested market, I would say all brands that came out with mirrorless cameras are its competitors.
Look at Olympus new OM-D and EPL5, both had m4/3 sensor that are no doubt smaller than the APS-C sensor, but its performance are stellar, I owed the OM-D and Canon's 7D, and their image quality are almost the same. Another thing about the m4/3 - their AF was incredible - fast and pretty accurate.
Then the Fujifilm's X-pro1 and X-E1 (or something like that), both had incredible sensor too which produce image that many swear to be the best in the line (not sure though, I didn't had the fujifilm).
Of course we have the Sony's NEX system. and do note that the Sony made one of the best sensors around... and had one of the fastest (or the fastest) autofocus in video mode.
Of course finally we are looking at Samsung... nothing to say here because I have no experience with Samsung at all... and none of my photography buddies uses Samsung, so yeah.
There are also the Pentax (k-01, Pentax Q) and the Nikon V1/J1/V2/J2. Well... except for the K-01, the Pentax Q and Nikon 1 series had very small sensors, that doesn't mean their low light performance is bad or something like that.
Anyway, my point is... do not just look at EOS-M... look to other brands' mirrorless camera, play with them for a while and see which one you like best, then choose that one. Also don't give the G1X a miss. Although it is not a interchangeable lens system, but its image quality is stellar.