I had a chance to check out the EOS-M with the 22mm, 18-55 EF-M zoom, and the EF Mount adapter with a 24-70 II. It handles fine with the 22 prime but for a longtime DSLR user, it felt awkward to zoom manually without a viewfinder. I know it's not for me; shooting through the LCD display makes composition harder and I had quite a bit more handshake holding the camera away from my face.
The lack of an eye-level (electronic) viewfinder is a challenge for me - no being able to brace the camera properly. Hopefully Canon will in due course launch a mirrorless body with an EVF (and hopefully a next gen APS-C sensor). I have no inclination to buy another camera based around the current 18MP APS-C sensor.
I wouldn't look at a mirrorless Canon until it has quality EVF. While the little tunnel optical viewfinder on the G-Series is a piece of rubbish, it's still preferable to composing and shooting with the camera at arms length like an iPhone. Errgh. Years ago I had a little Canon S3is P&S with an EVF. As far as EVF's go it was seriously entry level, but I didn't mind it at all.
I'd expect EVF's to mature pretty quickly to a point where they will be preferable to a DSLR optical viewfinder.