That's a nice review, and yes, one can certainly make nice images with it. That said, a couple of your comments remind me of its drawbacks. As you say, this camera - like other small cameras - seems designed for those who want to be "always ready for a quick 'grab' shot". And not just professionals like you, but (mostly, I suspect) casual customers who think DSRLs and other cameras with lots of visible controls are too big/complicated/hard to use/expensive.
Ironically, though, it seems to me that it's far harder to take a good "quick grab shot" with an EOS-M than it is with a DSLR. Why? First, unless the subject is large, accurate focus takes a fair amount of time. The M's focus box is far too big for smallish subjects (especially if you're attempting selective shallow focus) and, unlike M43 cameras (and others), you can't make it smaller and stay smaller from shot to shot; instead you have to use the magnify box separately for each photo. While this usually results in accurate focus (but not always - sometimes the camera has flatly refused to focus at all for me, even when the subject filled the magnified box), the process is far removed from taking a "quick grab shot"; what takes a couple of seconds on a DSLR or OM-D takes much longer on the M.
Second, and related, as you say IS is more important with cameras that don't have a viewfinder; all lenses would benefit from it and, as Panasonic has come to realize with its latest M43 bodies, it should be in the body. So you have to be extra-careful when holding the camera.
Third (this matters less to me) the camera is just slow to use - not only does establishing focus take longer, but there's quite a lag between when you've taken a shot and when it will let you take the next one (write time? maybe it's shorter if you don't shoot RAW, but I'm not interested in that); photographing action must be rather frustrating, street-shooting maddening unless you're happy with narrow apertures that get everything in focus.
Maybe I'm just not sufficiently accustomed to using it, but it seems to me that the convenience of its small size and weight comes at the expense of inconvenience of use. Considering that my OM-D doesn't have a comparable expense and, given the tiny size of M43 lenses, weighs even less, I'm not sure I'll be keeping my M.
SDSR, Yes of course all your points are valid for your style of shooting. Not taking its price into account and for a street shooter there are obviously better cameras out there.
I don't really do 'street' as we understand it but rather 'street portraits'. So an ultra fast AF is not that important for me. For fast Af I have a 5D2. In fact for me one of the best 'street' cameras out there would be the Leica X series. They have agonizingly slow AF but one brilliant redeeming feature which is a super easy 'zone focus' capability. Set up like that focus becomes a non issue...but then as you said you don't like narrow apertures. I on the other do like narrow apertures, so for me it would work perfectly.
I bought the Eos M purely as a backup camera for my 5D2. I tested the Af instore, and that's before the firmware update, and felt I could live with it. After the firmware update I am more than happy with it. So much so that I have decided to wait and see what the next Eos M looks like before committing to my other 'dream' camera, the Fuji X100s. The Eos M 'slow' AF is now a non issue for 90% of my images. Perhaps two and a half years with the even slower X1 has taught me to anticipate a bit more than most with more responsive cameras
But now that I have the Eos M I realize it is not half as bad as the press made it out to be, and with a little bit of work and foresight it can be a great little camera.
As for getting a 'quick grab shot' I think its eminently suitable for that because I have it with me all the time, precisely because its so small and because I also have an OVF for it. The Af is fast enough that I am more than confident of getting that grab shot when it arises...obviously your shooting style needs something different.
Yes it is slower from shot to shot than my dslr, but then when I expect 'action' then I put it on continuous and bang of a few...it works for me but obviously might not work for someone else...
For me its great strengths are compatibility with the rest of my Canon system and thus a good backup. Price..I got mine with the 22mm lens, lens adapter and flash for less than half the price of the fuji X100s. Size - I carry it with me everyday...and the better than expected image quality, but it requires careful processing. for my style of shooting it really is a almost perfect solution.
If I didn't have a Canon DSLR and wanted a small compact high quality and very responsive camera I would certainly have looked at the OMD and a few others. But I just don't like having too many different brands on hand and thus for me the Eos M has been a very good buy. I expected worse and actually got a lot more...And not being able financially to buy and sell cameras when they dont suit me perfectly I have to make them 'work' and bend their will until it fits in with mine...
And yes I wish Canon would have in body IS, it just makes a lot of sense! And I also wish a Leica MM was a lot cheaper!
Enclosed an image that illustrates my point. I saw that this guy was going to ride past me on the pavement. I just lifted my camera and waited for the 'action' to happen, my camera was set on continuous and I just let rip as he entered the frame. I would do the same for a 'street' shot as well...