I purchased the new Nikkor 18-300 mm (f/3.5-5.6) lens today and ran it through a bunch of test in various condition and the results are in… this is a great lens for $1,000 (US)! It maintains excellent sharpness even with shots done fully extended at 300mm, there is practically no darkening around the corner/edges, very low noise, and sharpness on close subjects is spectacular. Drawbacks… slight chromatic aberration on high contrast edges that are near the sides of the photo when shooting with longer focal lengths at 250 to 300mm. But even the chromatic aberration is very slight and easily fixable.
I tested a Tamron 18-270mm today as well, at about half the price of the Nikkor 18-300, the Tamron 18-270 was a big disappointment. I won't make this a Tamron bashing article, because I absolutely love my Tamron 90mm f/2.8 macro lens.
If you can't afford a really good two or three thousand dollar lens, the Nikkor 18-300mm is a great medium costing lens that will not disappoint at it's selling price!