I deliberately didn't post specs since there's a link to see it. But...
From what I can tell, control layout is mostly the same -- which 5D mk III users will probably like because they'll be familiar with (most of) the layout.
30.4 Megapixels. Improved metering (150,000 zones instead of 63 on the 5D III).
4k video at 30 fps. Full 1080HD video at 60 fps.
The ISO got a bump. The 1D X mk II got a big bump in dynamic range and is roughly neck & neck with one of the Sony's and ahead of everyone else (oddly enough... while Nikon tends to use Sony sensors these days, I expected the Sony & Nikon scores to be the same, but apparently not. (Is Sony holding out on Nikon and giving them sensors that are a generation behind?) The "rumor" was that this improved DR would also go into the 5D IV. They DID state that it has much improved signal to noise ratio (that's extremely good and an indicator that it probably did get the much improved dynamic range) and is a much better performer in low light offering greater detail in the darks. We'll have to wait for tests to see how that worked out. I did see a sample image of a night-scape scene shot at ISO 6400 and 60 seconds. While it wasn't noise free (I could easily see noise) it did look pretty good considering it was a 30 second ISO 6400 shot. Usually it takes some work to clean up such images.
There's the dual-pixel AF -- that was no surprise. My understanding is that now that Canon has this and it's working very well, it'll show up on every new model. It's been on the 70D and 80D. Early versions of it were even on Powershots. Of course, dual-pixel AF is only used if you're in video mode or live-view mode. I don't often use those modes so this probably isn't a big deal "to me" but might be to others. It has a new feature they call DPRAW and an ability to make some type of adjustment after the shot is taken. I was trying to understand what that really means and how it works. It also has in-camera lens optimization (corrects things such as CA). You could certainly do that in post processing but it can now happen in camera (probably a bigger deal if you shoot JPEG. I typically only shoot RAW.)
The rear-screen is touch-screen. No surprises there either. While they certainly could have done that to the 5D III because they had already done it to the T5i. But the concern was that while the T5i has a mostly consumer-oriented market who would probably like the feature, the 5D III is more of a work-horse camera used by pros, and they might *not* like it (pros tend to be very good at operating the controls quickly). So apparently they've decided that pros will like touch-screens and felt safe adding the feature this time around.
I noticed they can do HDR during video -- that was "interesting". I never shoot video. I think I "tested" video on my 5D III maybe once just to see how it worked, got that out of my system, and never really used it again.
GPS is built-in. NFC is built-in. Wi-Fi is built-in (actually it looks like it's on a removable card... I wasn't quite sure on that one.)
They moved some connections around... the side has three rubber flaps instead of two. They moved the remote (wired) shutter release port to the front lower corner instead of the side.
The CF & SD slots are now both high-speed slots (CFast and UHS-1 slots). The 5D III had CF & SD slots (both) but they weren't high-speed.
What I am MOSTLY interested in is the improvements in signal to noise ration (SNR). SNR is a big deal in astrophotography.
