I liked the Canon EOS M more than I expected -- but less than I should have. It's got a compact, well-built and well-designed metal body, and a responsive touch screen with a streamlined interface, and it delivers the photo quality you expect from this class of camera. But the feature set is pretty blah, and it suffers from lackluster performance. And the fact that there are only two native lenses for the system, an 18-55mm standard kit and a 22mm f2 pancake, makes it less attractive than the more established systems with which it competes.
Image quality
As is par for the category, the EOS M delivers excellent photo quality. JPEGs look clean up through ISO 800 and reasonably good through ISO 1600, though raw delivers better quality even at low ISO sensitivities -- better color and reduced edge artifacts. I didn't enable aberration adjustment during testing, however, which may reduce the fringing from the 22mm lens at wide apertures.
As is usual for all Canon's consumer cameras that predate the EOS T5i, the default Auto Picture Style boosts saturation and shifts some hues -- notably reds -- a lot more than I like. Normally I use Neutral on Canon cameras, but even that proved odd in the EOS M. Faithful seems to deliver the most neutral results, but you need to bump the sharpening up a bit.
Exposures are consistent with no surprises, however, and images look appropriately sharp; not too soft and not too crunchy. Unsurprisingly, the video bears a lot of resemblance to that of the T4i and T5i. It has nice tonality, but even more moiré and aliasing than the video from those cameras.
Performance
Let's just call the EOS M's performance...flawed. It's based around the same hybrid CMOS sensor as the Canon EOS Rebel T4i/T5i, which includes both the contrast autofocus sensors, the type of autofocus used in camcorders and other video AF systems, and the traditional phase-detection sensors you find in dSLRs. That's nice, but autofocus performance in ILCs has become extremely good of late, even in contrast AF-only models. And for some reason, it just doesn't work as fast here as it does in the dSLRs.
The autofocus is relatively slow -- the 18-55mm lens has notably faster autofocus than the more popular 22mm lens -- and the camera itself seems just a tad sluggish. It takes 2.9 seconds to power on, focus, expose, and shoot. To focus, expose, and shoot in good light runs 1.3 seconds (22mm) or 0.9 second (18-55mm), which is pretty slow; those times rise to 2.5 seconds and 2 seconds, respectively, in dim light. Two sequential shots run between 1 and 2.2 seconds depending upon lens and file format (raw or JPEG). While it has a seemingly fast burst of 6.6fps for an effectively unlimited run -- during testing it zipped past 20 shots with a 95MBps card -- and raw sustains 5fps for 6 shots, both of which exceed Canon's rated speed, that's without autofocus enabled. I didn't test it with Servo AF, but can tell it's a lot slower.
The centerpoint AF is fairly accurate, but like all fully automatic AF systems it routinely choose the exact wrong subject for the scene. Servo AF operates fine while shooting video, with just a little pulsing when focusing on still subjects. Though the screen magnifies the view for manual focus, like most cameras it doesn't magnify while you're recording; it would be much easier with focus peaking.
Even though the flash uses its own pair of AAA batteries, after firing two shots with the camera's battery level at 3/4, the camera battery dropped to blinking red. And it has a subpar battery life to begin with.