I've had mine for a couple of weeks now. I bought it as a successor to my 30D. My opinion?
- Autofocus - I'll deal with this first. If you're experienced with a DSLR you quickly learn how to work around the M's limitations in that department. I shoot my daughters sports (equestrian, soccer, etc.. ) and I'm getting better pictures out of the M than I did with the 30D. Read the manual, or, there's a very good YouTube video out there explaining the workaround.
- Buttons/Menu - Again, if your experienced shooting in manual, or AV mode, with a Canon DSLR, it is really easy to use the touch screen menu. I find it just as easy... in a different way. For those having problems - Read The Instructions for God's sake! I think that a beginner might find the touch-screen menu a bit overwhelming. One drawback is the body is so small that it is easy to accidentally change settings just by holding the camera.
- Viewfinder - Personally I don't miss my dim 30D viewfinder, and on the M I can pinch-to-zoom with the viewfinder to fine-tune manual focus, which is an amazing feature once you try it. The LCD screen brightness can be boosted to make shooting in the sunlight better.
- Lenses - I've got an investment in 'L' glass, so I bought the EF lens adapter. I don't notice any autofocus difference between the native lens (17-55 kit lens) and the EF70-200L, or the EF-135L. If I didn't already have the EF lenses though, I doubt I would have purchased the M.
- Picture Quality - I get the picture quality of a 60D/7D for a fraction of the price (499 $CAD with the 17-55 IS kit lens and flash). What's not to like. Noise reduction at high ISO is very good.
- Battery - I admit it. Battery life sucks. Especially since you have to crank up the LCD brightness when outdoors. You have to get a second battery.
The more I use the M the more I like it. Yea, the autofocus is slow, but actually it is almost on par with my old 30D. I love the small size, low weight, of the M. With the 70-200 attached, it handles wonderfully by holding by cradling the lens. It balances perfectly - better than the 30D.
If the firware speeds up autofocus, it will be perfect!