With the M6 Mark II Canon has taken the M series to another level of power and capability: Higher resolution, faster performance, and even better image quality than before.
Qualities of M6 I wrote about in my M6 review all apply to the Mark II as well. Beyond the M6 Canon has continued to reduce the performance and image quality gap with full frames: With the M3 or M6, when I felt I needed to generate the highest quality results I would reach for my full frame DSLR; but with the M6 Mark II, I don't.
To me the main reason to get an M series camera remains the small size; the Mark II is just a bit larger than the original M6 but still highly portable, and much easier to grab and take with you than say the 5DIV. I was initially excited about the Canon RP, thinking it would satisfy my "small camera" need, but in hand it is significantly larger than the M series.
I know some folks are disappointed in the lack of a built-in EVF on the M6 Mark II, but assuming that helps make the camera smaller, I'm fine with it. I have the original external DC1 which I occasionally use on sunny days, and enjoy the flexibility of having it be optional.
As far as performance, I've measured the M6 Mark II as capable of 21 shot bursts at 12 frames per second with an older CF card; with a newer Lexar UHS-II card I was able to get 14 frames/sec for 23 shots. On the M6 the best I saw was 17 shot burst at 9 frames/sec. These are with RAW shots; with JPEG you get much longer bursts, of course.
Some complain about lack of lenses for the M series. True, there aren't as many native EF-M lenses as say EF lenses, but there is a reasonable variety covering the 11 to 200mm range, including some highly capable ones, such as the Canon EF-M 32mm, 11-22mm, and the recently introduced Sigma primes. Of course all Canon EF and EF-S lenses are also available to use, with the EF-M adapter.
For instance the Tamron EF 150-600mm:
Full moon with the Tamron 150-600mm lens on the M6 Mark II, hand-held
Tamron also makes a smaller native EF-M lens which covers a practical 18-200mm range:
San Francisco from Sausalito on a foggy morning, Tamron EF-M 18-200mm at 189mm
Tamron EF-M 18-200mm at 42mm
Note that the Tamron 18-200mm, which I bought for the M3, did need firmware updates to work with both the M6 and the M6 Mark II. In both cases Tamron applied the fixes quickly; with my only out-of-pocket expense being the shipment out.
As mentioned above the Canon EF-M 32mm is a wonderful lens:
Spider with the EF-M 32mm. Prior to the M6 Mark II, I would have reached for the 5DIV for this shot.
Despite the increase in resolution (from M6's 24MP to 32MP, highest for an APS-C camera I believe), The M6 Mark II is very good in low light:
Black cat in a dimly lit room? No problem for the M6 Mark II with the EF-M 32mm attached. ISO 6400.
And another cat, as a part of a series of shots with the EF-M 32mm at ISO 3200. Here I was able to quickly reach for the camera and grab a series of about 20 shots before she noticed me and left in a huff:


Lucky the cat can't believe I disturbed her cleaning session.
Since the M6 was already a pretty capable camera, at first I was hesitant about moving to the M6 Mark II; however, the higher resolution and the positive pre-review write-ups won me over. I'm glad I upgraded; the M6 Mark II is a better camera than the M6 in almost every way.
If you have an earlier M camera that you use, consider upgrading to the M6 Mark II. Other than the cost of course, the only sticking point is likely to be the lack of built-in EVF, for those of you who can't do without it.
If you have a Canon full frame, the M6 Mark II is a very capable companion for cases where a smaller camera is handy, and it ability to share lenses with the bigger sibling is a bonus.
For my needs the M6 Mark II ticks all the boxes, so gets 5 stars.