I have the Tamron 28-300mm with VC (for nikon), and that review (for the 18-270mm) might well have been written for my lens - seems to match my experience exactly (other than comparison with other similar lenses, which I've not done). I have managed some pretty decent pictures, but have been thankful for the VC - to counter the distinct shake at the super-zoom end. The auto-focus is slow, particularly in lesser light or at the far end of the zoom : no wonder, as the aperture shrinks to 6.3.
It was a blessing while out on vacation : not having to choose between lenses for a group picture (wider angle) or the close-up of a sleeping sloth on a tree.
But if I knew what I'd be photographing, I'd rather choose specific lenses (the 17-50mm 2.8 for indoor parties, or the 70-300mm for soccer games). Those are definitely sharper than the all-in-one 28-300.