I'm writing this review as a hobbyist rather than professional photographer (that is, that sells photographs for a living). My first 5D was the Mark II, and I've used the Mark III for over 3 years myself, and instead of going through all the nitty-gritty of the Mark IV which you find elsewhere, I'm going to speak to mostly to the differences I've found in my day-to-day experiences and whether it's worth the upgrade for the hobbyist.

First off, coming from the Mark III, the IV on the outside is very much similar, and you could mistake them at a glance. The differences include a slightly rougher cap on top of the new Mark IV body (where the Canon brand label sits) whereas the Mark III had the same material extended from the body over the cap. Perhaps it's a new material housing to play more nicely with the GPS/Wi-Fi? There's also new switch to toggle face detection in Live View mode in the back. The mode switch dial is also the newer Canon styles that bumps up a bit rather than the more flatter design of the Mark III. Otherwise, for those coming from the Mark III, you can feel right at home picking up the Mark IV for the first time.

In terms of shooting, I personally find the viewfinder to be brighter on the Mark IV than on the Mark III. This could just be my units and maybe a bit of dust on the Mark III, but using the same lenses, I find the Mark IV viewfinder a joy to use, much like the Mark III's, and even a shade brighter! The new Dual Pixel AF works as advertised, and is much faster than the Mark III at face detection and toggling between different subjects - a big improvement here. The back review LCD is also a touchscreen now, which allows for your standard panning of shots as well as pinch-and-zoom. Although many shooters will still opt for the familiar mechanical buttons, as a hobbyist that shares the camera for others to shoot as well as reviews them on the spot with many moms with Android/iPhones, it's so much easier now to have them use the touchscreen to flip from photo to photo, and to zoom in and out to see themselves and whether the shot is worth keeping ;)

In terms of photo quality, the highlight is the improved dynamic range of the new 30MP sensor. Although improved from the Mark II to the Mark III, I see a marked improvement for the Mark IV. Pushing exposure on underexposed shots with the same ISO produces less banding on the same shots with the Mark III. Although Canon is still behind Nikon in this area, I'm happy to see improvements in this area. Auto-focus at lower light levels at the center point is also improved, so that helps with getting those low light shots as well. As for overall crispness and quality of the shots (which of course, depends very much on the lens itself), I found photos were very similar on the Mark IV, which is not in anyway a let down given I thought the Mark III was overall excellent in terms of stills quality.

Also as a hobbyist with a simple Lightroom workflow, I still have Lightroom 5. With Adobe's latest Camera Raw 9.7, Adobe now supports the Mark IV, but you'll need the newest Lightroom 6 or Lightroom CC, which is another cost to add to your upgrade tally if you don't already have those versions and plan to use Lightroom. Also, although Adobe will enable editing of the new Dual Pixel RAW format in Lightroom, it looks like, at least for now (as of late September 2016), it doesn't support any making micro-adjustments in focus that can be done in DPP. I find that it's useful when shooting with fast primes like the Canon 50 f/1.2L where small adjustments can help you hit focus.

Overall, another superb iteration of the Canon 5D line that hits many of the upgrade checkboxes, most particular in the area of dynamic range. I'll update my review as I've gotten more behind-the-lens time with the Mark IV, and in particular, video shooting. So, is the upgrade worth it for Mark III owners? I would say for those of you shooting in more low light settings, the upgrades could make the additional cost worth it for you. However, for many others, given that photo quality improvement from the Mark III is not revolutionary, I would say it may not be at the current MSRP for Mark III owners; maybe wait for the next Black Friday sale to bring the price down a bit. Also, having used the Mark II as well myself, for those Mark II owners itching for the next big thing, with two generations of technology under its belt, the Mark IV is a worthy upgrade that you don't have to worry looking back on!