I hope elm58 will tell us some more of his experiences with the 200-400 lens, when he has been using it for a while.
Hi Eldar, I'll give it a go, no review, but my experience to date.
On Nick Brandt, I agree, what an amazing Photographer, I've tried to replicate his work, no success, I've bought his Books and as you say, amazing Images but no indications on how he does what he does, although he does say he doesn't use PS to achieve the results.
I've had the 200-400f/4 from day of release, had a Pre Order in at Cathay Photo in Singapore a year prior to actual release.
To date I've had the Lens on 3 Trips/safaris, Northern South Africa (Mala Mala & Londolozi) Tanzania & The Serengeti and recently to Svalbard.
When I first picked up the Lens, I ran alongside Tests against 4 of the other lenses that I own/owned at the time, 200f/2 L, 300f/2.8 L II, 400f/2.8 L II & 600f/4 L II, I tested each Prime Lens at f/4 & f/5.6 and then shot the 200-400f/4 at similar lengths & f stop (i.e. 200f/2 @ f4 & f/5.6 against the 200-400f/4 @ f/4 & f5.6, 300/400 & 600 Primes same).
What I wanted to see was how the Primes compared against the Zoom for straight sharpness when shot at similar Length & f stop.
Not scientific in any way, just a hands on Test I could conduct at home, I shot the same subject all the way through (A flowering Plant) rather than a Test Sheet.
The results for me showed what I expected to see, The Primes are sharper, but I was surprised at how Marginal that sharpness was, the 200-400f/4 is a very sharp Lens even comparing against the Primes.
I next tried to compare the 200-400 ability to lock Focus when compared to the Primes, to evaluate this I simply had my Lads ride past the front of my House, for about an Hour while I compared the Focus Lock merits of Primes against Zoom.
The Standout Lens was my 300f/2.8 L II, nothing in the listed lenses Locks on as fast or as accurately as this Lens, among the remainder, the 200-400/200/400 & 600, there's really nothing between them, they are all excellent Lenses for Speed of Lock On and Accuracy.
I've now shot the 200-400f/4 on the 3 trips mentioned earlier, that's 30 thousand Images with the 200-400f/4, against that I've had either/and the 300f/2.8, 400f/2.8 or the 600f/4 alongside on a trip (not all Lenses on all trips), but the 200-400 + one of the other Lenses (although I always bring the 300f/2.8 ).
The only place I find the f/2.8 an advantage, is Low Light, dawn/dusk, and the ability of the f/2.8 Lens to Lock Focus quicker than the 200-400f/4, and that makes sense as the Lens is Focussing wide open and doesn't shut down to the chosen f/stop until you actually take the shot, so the f/2.8 Lenses are able to focus using twice as much light.
But where the 200-400 absolutely murders the Primes, is it's sheer versatility, the ability to be at 560mm f/5.6 then begin zooming back all the time keeping the subject locked in focus, perfectly framed to reduce the need to crop, flip the converter out at 400 and Zoom back out to 200, all with the same Rig.
Previously to do this I had 3 Rigs set up, 1Dx + 600, 1Dx + 400 & 5DMK3 + 200 (or 300) and I found myself exchanging Rigs as the Subject moved closer, or farther away, workable, but a PIA.
For the style of Photography that I personally prefer, Wildlife, the 200-400f/4 is a must have Lens that is as Sharp as you need, Locks Focus amazingly well and the finished Images require less cropping etc.
I still use my Primes, the 600 + 1.4x Converter, the 300f/2.8 L II for those Dawn/Dusk shots, I'll be buried with my 200f/2 but I've sold my 400f/2.8 L II.
If I had to choose one of these Lenses to keep and use only that Lens ?? I wouldn't hesitate keeping the 200-400f/4, fortunately I don't need to make that decision.
But, if I was a BIF Photographer, it would be the 600 + 1.4x the 200-400 isn't long enough for small birds, and the 600 + 1.4x (840 @ f/5.6) is still slightly sharper than the 200-400 with 1.4x in place (560 @ f/5.6).
I've tried the 200-400 with built in 1.4x engaged + 1.4x Converter, Images are Ok, not great, Ok.
With the 200-400 with built in 1.4x Engaged + 2x Converter, Images are simply horrible.
If your into Sports Photography ? 200-400f/4 is a great Lens, but you may miss the f/2.8, 400f/2.8 may be a better choice.
Wildlife in General, my view the 200-400f/4 is the best Lens available.
BIF, maybe the 600f/4 plus the 1.4x
Hope this is of some use in any future decision making for you, I always liked the nikon 200-400f/4 and was amazed Canon just hadn't produced one, I'm glad they held of as I believe the Canon 200-400f/4 (1.4x) is a step beyond the Nikon Lens (and I have tried them side by side, 1Dx + 200-400f/4 and D3x + 200-400f/4).