I got this lens as a kit lens with my D5100 (along with Nikon/Nikkor AF-S DX 18-55mm f/3.5-5.6G VR lens). This is not a technical in-depth analysis of this lens; only simple words for beginners.
I was (infact I'm) happy with D5100 and the 18-55 but this 70-300 truly disappointed me. This lens has no auto-focus and for the focal length range (70-300mm, on DX bodies it becomes 105-450mm effectively) - absence of VR makes it more difficult to handle. I tried to get rid of the VR issue at highest focal length (even I tried at lower focal lengths) by using a tripod and remote, but then many times the subject was out of focus.
This lens is AF lens, AF mount lenses do not auto-focus when mounted with entry level Nikon D-SLRs like D5100, D5000, D3200, D3100, D3000, etc. Amongst the DX bodies, D7000, D90, etc. (with in-built focus motor) are capable to perform auto-focus on AF lenses.
This is (absence of in-built focus motor) a major dis-advantage of D5100 (a superb entry level SLR), but at the given price range it is acceptable. Entry level DLR owners should make sure that, they are purchasing only AF-S lenses, which can auto-focus successfully on their cam.
This lens is bit heavy (more than 400 grams) and that makes it more difficult to handle - without a tripod there is always vibration issues untill and unless you really have a firm grip. So, even if with high end cameras (cameras with in-built focus motor) the auto-focus issue can be eliminated; but absence of VR will trouble alot at the given focal lengths [Nikon cameras does not come with in-built sensor shift VR/VC mechanism, that is one of the best attributes in SONY Alpha cameras].
May be professionals can make awesome snaps out of this lens but for me it was total disappointment. I will surely not suggest this lens to any beginner - the shops normally fools around by including this cheap lens in a package, the specification sounds big but in reality it is of no use.
Therefore, out of 5, I will hardly give 1 point to this lens - NOT recommended.