I thought I would write a review after having now owned it since late 2016 when it came out. So this is sort of a long time review.
So do I like it? Yes I do. In fact I just recently purchased a second one.
This is all from a stills point of view. I pretty much never do any video.
So here is my journey to date. I started as someone who always wanted to learn photography. Got obsessed and picked up a 5d2 along the way. I eagerly waited for 5d4 to come out and did the upgrade which was a big one. I got asked to shoot a wedding and have been hooked ever since. I love the challenge of shooting weddings and I have been studying the art of photographing people, which is an amazingly complex subject when you get into it. Anyway.... This is what I think hitting the main points that I consider important.
Image Quality: This is why I like it. I love the files that come straight of the camera. They are really beautiful. I basically do not have to do much at all to get where I want to get in PP. I import them with a basic preset I made and do some tweaks and that's it. The colours are nice plus it has an intangible quality that I do not know how to put into words that I really really like. I could not care less that it may or may not be a stop better of worse in terms of dynamic range. I see videos of someone photographing something 5 stops underexposed and lift the shadows and whine about the results. I don't get that. I do understand that landscape and real estate photographers appreciate as much DR as is available, but for most of us I do not understand the obsession with this spec.
Having said all that the Dynamic Range is great. I can recover shadows if I make a meal out of an exposure or if I am too lazy to setup up some lighting.
As an aside I tried a Nikon D800E along the way as a possible second camera. The nikon was a fine camera took awesomely sharp photos, worked well but I did not like the images as much as the 5d4. They were too green and magenta on skin. I concede this is lack of skill of my part as many photographer I greatly admire use Nikon and their photos look amazing I gave up and moved on.
AF: I never miss with this. I generally shoot in single shot 90% of the time. It focus's great in low light and honestly it never misses unless I mess it up. I find it remarkable. Shooting at 1.4 is always in focus. Also for a hack Macro photographer like me it makes it really easy. Also there is a bottomless pit of way you can set up the focus options. There is a dude on Youtube that runs through all the options.
Build: This is what I like about Canon and Nikon. They are tough and just work. I have never had a serious problem with it. It always works, the buttons always feel great. I place a really high value on reliability. Nothing sucks more than a buggy or unreliable product. Having said all that I have twice been unable to view images on the back of the screen if I hit play. This was after a full day of shooting, changing lenses and shooting about 800 to 1000 photos. If I power cycle it it goes away. It has not happened since I firmware updated it. I suspect it is some odd bug from a series of actions through the day. If that is all I have to worry about that is ok.
Live View: Really nice screen, looks great. It is something I use occasionally if I am holding the camera over my head or if I want to eyeball exposure if I am not sure. The face detect feature is really good. I am pretty sure it focus's on the eye. I am surprised that this was not more heavily marketed like Sony have done with their awesome eye detect.
Frames Per Second. 7 is enough for what I do and I would imagine for the majority of other people. In fact I really never use it and even then I do not really need it. I actually find I get better shots if I do not use it and anticipate shots.
Flicker Control: This is solid gold when you need it. I seem to need it a lot. Works great.
WiFi: Works fine. I personally the software for the phone is clunky and cumbersome. But is great for when I put the camera on a monopod up high or to do ground level shooting or whatever. Also super useful to get images on your phone and up online. I do this a lot shooting events when trying to beat everyone else getting images up.
Low Light High ISO: Really good. Obviously the lower the ISO the better but I have zero problems going to 6400 and 12800 in a pinch. Plus the noise when present is not terrible. The main thing is that the light is nice light. I have shot at 32000 as the sun has gone down and the file looks amazing as the light is ambient and not mixed. . The issue as always is in mixed light it will make your high ISO files look terrible.
Flash: The one thing that never seems to get talked about is how well it implements flash. It really is outstanding.
Ergonomics: I think this is a preference and what you start out with. But I think it is excellent and very intuitive. I wish the body was a little bigger so my pinky finger has somewhere to sit better to avoid hand fatigue rather than have to use a grip.
Value: I think it is overpriced considering what the competition is doing. But you have to take into account the total cost of ownership. Lenses are cheaper than Nikon or Sony. Plus the entire eco system is outstanding. Especially when you get into strobe land.
The competition?? I look over the fence at cameras like the Nikon 850 or Sony's latest offerings and I must admit I have spec envy. It feels like Canon is getting eaten by the competition. However the way I shoot, the extra specs honestly would not benefit me. I think the pros of the entire Canon system outweighs a few tech benefits that say Sony offers. Personally I would not change as I love the lenses and as I said I love the images straight out of camera.
The future? Personally I hope the 5d5 is a mirrorless camera. The main main thing I want is to see exposure in the view finder but have the canon files. The other benefits would be neat like IBIS and the Silent Shutter.
Summary: I think it is a awesome jack of all trades camera that is tough and reliable and produces outstanding images. If you can't get good photos with the 5d4 then you need education , not a marginally better camera.