Maybe I have looked close enough. I regularly make 12x18 prints and occasionally 24x36 prints. They are quite sharp with no perceivable issues. However, I will admit to not peeping pixels. That in itself is a waste of time.
As you probably know, making larger prints that look good is not a criterion for lens quality or sharpness. At 24x36 you can't peep pixels unless you are a member of the raptor species.
It's the reason why you can take an iPhone image and print it to billboard size and it will still look great.
My issues with this lens are the following:
Terrible edge and corner sharpness - not great for landscape
coma - just bad to have a lens with bad coma
chromatic aberration - yes, you can use CA correction, but that adds another step
vignetting - again, this can be corrected
distortion - pin cushion and barrel - also correctable to some degree
bokeh - totally dreadful and busy - not correctable
focus breathing - who wants a lens that is promoted as a 300mm at maximum zoom that can barely manage to return a field of view equivalent to a 135mm lens -
no tripod colllar- making it a challenge to use on a tripod.
no dust and moisture sealing - it is a fair-weather lens - and not one you'd want to take to the shore, particularly on a windy day
cheap feel, slow handling, etc
And the worst part - it costs $1000.
I wanted to love this lens when I first considered getting one - I borrowed a friend's copy for a day - hated it. Then I waited almost a year and borrowed one from NPS program - had it for 2 weeks - hated it. Fast forward to last year, when I borrowed one from another friend - hated it. To Nikon's credit - they were all consistently awful, and in the same ways. Good to excellent QA, awful design and engineering.
There is a good thing though - most of the issues with this lens are at the periphery of the image - making it almost reasonable to use on a crop camera. The center portion of the lens isn't bad. It is also much better on a 12 mp camera than a D8XX camera - which really reveals it's flaws.
The concept of a "walk around lens" eludes me. There are so many compromises in the reality of a walk around lens - I'd rather spend a little more and get two lenses that are better in quality, even used. I have a great "walk around" lens - an old 28-105, F3.5 - F4.5 - that I paid $120 for. It is quite sharp, gets me to 1:2 magnification, is small and light and it covers an FX sensor very nicely. I actually like it better than the wider zoom range 24-120 F4. I don't need to walk around with a $1000 28-300 mm lens that is awful at 300mm. But that's just me. Truth be told, when Nikon builds a "better" 28-300 I might buy it. If only there was a way to convert the Canon lens of the same focal length to Nikon mount and retain all the auto features and communication with the bodies. . . I wouldn't mind paying $2200 for one of those.