Fast auto-focus, very sharp (is there something sharper than a tack? If I had another cliche I would use it.), amazing OSS. I was afraid it might be too heavy for my aging arms, but the OSS compensates for my deficiencies. It's a little slow, but the available high ISO on my 7R3 permits shots in relatively low light. I live in the foothills in Colorado, with elk as frequent neighbors. The attached pictures were shot from my kitchen and office windows. The elk were anywhere from about 20 to 50 feet away.

I had a Sony 70-200 f4, which works well for general tourism photos, but fell short for wildlife. I bout this lens with X2converter.it works great

Contemplated purchasing the Sony 200-600mm but glad it was out of stock during decision. Shot for the first time this past Sunday in our sanctuary (no flash) and was pleasantly surprised on the detail of this lens. I used my Sony A7iii. I have a Sony 1.4x teleconverter and can't wait to see the magnification once I used it to get my original max distance of a 200-600. I have a 70-200mm and the weight is equal.

I have been taking pictures for 60 years, from a Kodak Brownie, to SLR, to SLT to mirrorless. This lens paired with the Sony A7Riii takes my photography to a new level. The lens is as sharp as any I have used. The optical Stabilization is unbelievable. Co-ordinated with the stabilization in the camera I can hand hold at 400mm for less than 1/100 of a second with out visible shake. It is clear that my 70 year old hands can't hold a 3 lb lens that steady but the stabilization of lets me do the impossible.
If I had any negatives it would be the weight of the lens. But it is expected in a long lens of that quality. Also the fall off of the lens is less than I hoped for meaning I need to blur many shots in processing. (I never thought of complaining that a lens is too sharp).
Sony has outdone itself with this lens.

Very sharp through the focal range. Just as sharp as my primes. Little on a heavy side (3.1 Lb) but very well balanced. If you use it with 1.4X teleconverter it only loses 1 stop but sharpness is still great.

I've mostly shot small objects at close range, (birds at a feeder, window frost, mushrooms), using a SONY A7RII camera. The results are sharp. I like the convenience of being able to toggle the auto focus and steady shot on/off using the lens switches. Manual focus with peaking is necessary when working with difficult to focus subjects like window frost. The removable tripod mount enable comfortable hand holding. The lens hood has a sliding opening whereby you can rotate a polarizing filter with the hood on.

Amazing lens, super sharp with quick autofocus. You will not be disapointed

I’ve owned each iteration of Canon and Nikon 100-400 both versions 1 and 2. This is every bit as good if not better. Sharp as a tack, easy to use. Shot it on a Sony A7rIv. Detail was amazing. Few OOF shots due to user error. Shot various dogs running across field and straight at camera. Love this lens.

Honestly, I have been a little slow to warm up to this lens, but it fills the need for a longer zoom. The slow-to-warm part is probably due to the fact that I purchased the 70-200 /2.8 GM first; its focusing speed, wide aperture, handling, and outstanding performance make that one a tough act to follow.

However, the extra reach of the 100-400 GM is worthwhile, and it performs amazingly well. The attached pics from a high school football game were shot from at least 20 yards past the end zone, so total distance was about 80 yards. I was focusing on the referee facing the camera. (Using a7R3 @ 400 mm, f/5.6, 1/1000th, ISO 400. No extender. Larger photo is already cropped to get rid of excess empty field to the sides.)

Positive points:
- Image quality is excellent.
- Focus is quick, accurate and silent.
- For longer telephoto work, performance is equivalent to the 70-200 /2.8 GM plus 1.4x extender, but with more reach on the long end.
- If you want even longer, the two available tele-extenders are compatible.

Is it perfect? No, nothing is.  There are a few design compromises as noted in other reviews, but they're just things to know:
- Focusing speed slows as light falls off. It is still quick but the difference is noticeable.
- Lens is a little bulky and the extending barrel adds to that impression. But it goes out to 400 mm! ...
- When carried facing down, the lens can extend due to gravity. You can tighten the friction ring to reduce this, but there is no solid lock.

Sony made an excellent lens at this price point. Basically, if you need to shoot photos in this focal length range, you will be happy with the Sony 100-400 GM!

I purchased the 70-200 f4 before this lens came out. I'm not a big zoom person because of the weight. Sony lent me this lens for a shooting trip to the Palouse. Never thought of hand holding this zoom but was amazed at the sharpness when I did. The optical zoom is beyond your wildest expectations. This lens is worth every penny.