This is a unique lens, presently - there is nothing else currently like it. Sharpness is excellent as are colour and contrast. It combines the popular 70-200 range (almost) with the equally popular 300 and all at f4. So it is two lenses in one. Flare and CA are well controlled. Has FTM and HSM, is a constant length and is made of metal - very solid lens which is upto the rugged outdoors. Though it is handholdable, a tripod and good tripod technique can give better results.
I too saw the PP review and note the field test and conclusion here:
"In the field: Test slides were very sharp and contrasty from the center to the corners at all apertures at all focal lengths, with the exception of f/32 at 200mm and 300mm, where the corners were slightly soft. Light falloff was gone by f/5.6 at all focal lengths. Flare was very well controlled at all apertures and focal lengths, with no ghosts.
Conclusion: After you get past one slight weakness—close-up performance at the longer focal lengths—what you're left with is an exceptionally sharp zoom lens with top-notch mechanicals, well worth the price."
Now that fits with my experience and that of 99% of others of which I have read. Unrealistic expectations and/or a bad copy(s) can make a lens look bad.