Image and build quality, focusing performance, reach.

Price, weight, price, bulky showy case, price, lack of VR and price.

I use this lens for wildlife and occasionally sports, on its own or with tele convertors it produces very good results even wide open. Stopped down its even better but there is seldom enough light for that. Its fast for its length and the tripod collar and mount are well designed so it balances with both my D2x and D200 by using different mounting points. It comes in a sturdy case with 2 rear element filter holders. However the case screams "expensive lens please steal so I keep it in a holdall. The hood is 2 piece and fiddly but keeps the folded length down. In place of a lens cap is a lens cosy affair like the 300. This does a good job but is slow to use.

I don't think anyone could hand hold this effectively so the lack of VR should not be such an issue BUT especially with Tele convertors even on a decent tripod let alone a monopod it can exhibit shake, Bear in mind with the 2x convertor on a digital SLR it works out at 1800mm 35mm equivalent and its f8 by then so shutter speeds are seldom that high. It's too expensive to justify and it's often not taken because of the weight but it does get you close to the action.