I recently bought an M10 when Rakuten had their 20% back sale. $449 with a $90 credit for future purchase was too good to pass up.
I definitely wanted the body and was interested in the lens but since I already had the M, M3, and 4 EF-M lenses, it was not a priority purchase.
As soon as I started playing with it, I was thrilled. The ergonomics make this the best M yet (although I never shot with the M2).
The buttons have a better tactile feel (play, menu, and set are slightly domed) with nice action. A rear wheel would have been nice but I don't miss it much with the logical layout and the front wheel is much better than the M3 with smooth easy rotation and positive well defined detents. The M3 front wheel in comparison seems stiff and prone to binding with vague mushy feeling detents.
I had grown to like the M3's EC dial and thought I would miss it but in Av at least, I find EC easier to adjust on the M10. The front dial defaults to aperture and you press and release the up button to switch the dial to EC. After adjusting, you can reset to aperture by hitting the up or the set button. If you shoot without resetting, it will remain in EC after the shot. It feels very natural to roll my thumb onto the up button, my finger is already resting on the front dial, and I am already looking at the screen to verify my adjustment. With the M3, I have to substantially adjust my grip to turn the stiff EC wheel and tilt the camera to see the top of the dial. I think the M10 will be less prone to unintended adjustments as well.
When shooting in M with auto ISO the up button scrolls horizontally between shutter, aperture, and EC. I wish you could customize it to toggle between shutter and aperture and then use a screen tap to access EC. If you set ISO manually, the up button toggles between shutter and aperture and you tap ISO on screen to adjust it. When you tap an on screen function (shutter, aperture, EC, or ISO), you can adjust by sliding a finger on the screen, using the left/right buttons, or turning the front dial.
Playback works nicely for me as well. The play button is terrible on the M3 and but the M10 is even better than the M was You can double tap for 3X zoom and double tap again for zoom reset. You can zoom in/out at any time with the front dial. I wish you could program the double tap for 100% and program it for point of focus or at least point of tap. After owning a 7D II, I am spoiled by how good it was but this is the second best I have had for quick access to verify focus accuracy. If you want to reset zoom while remaining in playback, you use the menu button just like the M3 and Powershots. I am used to using the play button like the M and DSLR's but I would be happy either way if only Canon would be consistent.
There is almost no customization available and some other things missing as well: no exposure bracketing, no rear dial, no "my menu", and no hotshoe. If you can live without a few things, it is really a beautifully engineered camera with a fast, friendly interface. It does need a grip, and I have a Flipbac G4 on the way that worked well on my M. I sent an inquiry to Richard Franiec to see if anyone has tried his M grip on the M10, I think it would have to mount closer to the lens since the M10 body is rounded at the edge. I like the thumb rest better than the M or M3, it is bigger than the M's and stiffer than the M3's but still has a grippy rubber texture. I like the flip up screen better than the somewhat sloppy dual flip of the M3 since I almost never used the flip down option and the M10 feels much more precise and stays tightly closed so that if you don't use it you can hardly tell it is there. The size is almost identical to the M except for being a little thicker.
If you haven't noticed yet, I am now an M10 fanboy - Canon can do no wrong! Time to sell the M3 and A6000.