Now that I had the opportunity to use this lens and the older styles - In fact I first acquired a 300mm f4 when I was shooting film with at Nikon F3, and had upgraded twice since. I can attest that this is the finest 300mm f4 to date Nikon has released.
People reported it was a small light lens but when I opened the box and pulled it out I said no way and my amazement did not stop there. Out in the field I found this lens so responsive, sharp, with excellent contrast that I instantly fell in love with the lens.
I have used Sigmas, Nikons, Tamron and Tokina of all similar reach - this Nikon is heads above anything I have ever placed on my camera body in the 300mm range. It just WORKS and it works well.
It is remarkably light and short for a 300, in fact I feel like it adds speed to my shooting. Mass: less mass = faster response to your inputs, making this lens a turn and burn lens with the ability to keep up to your pace.
Phase Fresnel - Nikon's first use of this element and in my opinion you will be seeing more lens with it - Hugh weight reduction while maintaining sharpness and colors.
All the details about the lens is remarkable, and it is not until you use it you understand what I mean. Imagine using a 300 that you actually don't mind carrying all day. This is my go to lens when I want to fly out without being over burdened physically. We all have those days when we just want to go out and shot a few without having back problems.
Using the Nikon Teleconvertors with this F4 - I find the 1.4 the most reasonable match overall with only marginal loss of performance. While the 1.7 is use able with additional hit in focus speed and the 2x may be pushing it for some camera bodies.
I hear other reviewers all the time make remarks like "image quality" suffers, or they are not usable. I say, even with my most expensive fastest 2.8 it is all in the technique. If you have nailed the basics you get good results.
As far as sharpness goes for any longs - I have never taken a sharper hand held image than one taken from a tripod or mono pod, enough said.
There are cheaper alternatives out there, and I have not bias to that, but if you go with a 300mm f/4 - I highly recommend this one.