Nikon has a long history at trying to perfect the mid-range zoom, and it dates all the way back to things like the 1963 introduction of the 43-86mm f/3.5 zoom (technically that would be a normal-to-modest-telephoto zoom). In the film autofocus era that got started in the early 1980's, some variant of 28 or 35mm to 70 or 85mm gained popularity, as this was within the design capabilities at the time and satisfied the "three in one" aspect most mid-range zooms have to deliver. Almost every maker ended up with more than one variation on this: just enough wide at the one end to be called wide angle, just enough telephoto at the other end to be called telephoto, with lots of "normal" in between ;~).
Tamron was the first to popularize something that went beyond the mid-range zooms, the so-called superzoom (lots of focal length range). Their original 28-200mm was compact and provided pretty much all the focal lengths a user might want most of the time. The lens was so popular it was the first lens to sell a million units (though I believe that was across several minor model changes).
Most of us called the mid-range zooms and superzooms "convenience lenses" when they first arrived on the scene, and I'd say the same thing today. Most people tend towards mid-range zooms (or superzooms) because it's convenient. You end up with one thing to carry (camera plus lens). You don't have to worry about how to carry more lenses, keeping track of lens caps, worrying about different filters for different lenses, the list goes on and on.
But with convenience comes compromise. Early on that compromise included image quality, though that's largely a thing of the past. Today's convenience lenses (again, mid-range zooms and superzooms) are pretty competent in terms of image quality. But you have to watch out for several types of compromise that sneaks in on your images when you use such lenses:
- Low light. Except for the big, expensive, and heavy f/2.8 versions of these lenses, one thing you almost certainly give up is fast aperture. It's not uncommon to have f/3.5 at the wide side and already be down near f/5.6 in the "normal" focal length range of such lenses. Certainly by the time you get into the telephoto range you're at f/5.6. This is a bit insidious compared to prime lenses. Consider a 35mm f/1.8 prime lens, a very inexpensive DX lens. It's at least two-and-a-third stops faster than any of the non-f/2.8 convenience lenses. That's the difference between needing ISO 3200 versus 640 in low light.
- Depth of field. That smaller aperture means that you have a tougher time reducing busy backgrounds to a blur; you may get more front-to-back focus depth than you want.
- Static perspective. Because you can zoom in or out from any position, you never move position. Need a detail of the plaza? Zoom in. Need the whole plaza? Zoom out. Want your honey standing in front of the fountain? Middle of the zoom range. There, see, you didn't need to move a foot.
One of the reasons why people gravitate to the f/2.8 mid-range zoom (currently the 24-70mm) is the first bullet, above. Some do so also for the second bullet. But the third bullet isn't being addressed as long as you stay put and zoom instead of move. So if you're going to get a mid-range zoom or superzoom, be careful this doesn't make you lazy in your shot selection. If you're zooming instead of moving, you're getting lazy. One thing you can do is to consider your zoom a multi-focal lens, not a zoom. Pick three focal lengths (e.g. 16mm, 35mm, and 85mm for the 16-85mm DX) and only use them. Think of your zoom as a wide angle (16mm), normal (35mm), and telephoto (85mm) and pick the type of lens you want before trying to frame the shot by pre-zooming to that focal length. Then bring the camera up to your eye and use your feet to help frame, not the zoom ring.
A lot of those switching from film to digital did something interesting: they kept using their basically FX mid-range zooms on DX bodies. Thus, I notice a lot of 28-70mm, 28-85mm, and 28-105mm lenses ending up on DX bodies. That makes them really 42-xx lenses, or normal-to-telephoto, not midrange. But this also means that those users don't often have any wide angle capability. Funny thing is, they didn't miss it because they didn't really know how to use a wide angle lens. If I could break photographers from any bad habit it is this: shooting only at eye level and only using a zoom to get closer. These folk are doing both those things. They never shoot at anything other than eye level, and they think that the purpose of the zoom is to simply get the shot without moving their feet. All of you who did my homework assignment during You Week know what I'm talking about here, so I won't belabor it.
Am I against mid-range zooms? Not at all. I've got a few myself, and they are very useful in a lot of situations. For photo journalism and sports, for instance, you often get stuck in a single position, and then the only way you can vary the shot is by zooming. That's not what I often want to do in that situation, but it's all I can do. There's a difference.
And mid-range zooms and superzooms are indeed convenient. All of us like convenience. Just make sure that the convenience doesn't take precedence over everything else. When it does, your images will start to suffer. Note that almost every pro has a convenience camera (usually in their pocket). That's why we all wanted better, larger sensor, compact cameras. (The Canon G1x is one such camera.)
I am a little more against superzooms than mid-range zooms these days. As good as the Nikkor 18-200mm, 18-300mm (DX), or 28-300mm (FX) are, their image quality compromises do start to show up when you put them up almost anything else that covers less focal length range. And they aren't as long in the telephoto end as anyone seems to think they are as you start bringing focus closer than infinity.
I'd argue these days that if you want a versatile all-in-one lens that it needs to be something in the 24-105mm range (FX; that's 16-70mm DX). Why? Because, as I noted in my article on wide angle lenses: as we've started printing larger and as we've been accustomed to the 28mm and 35mm perspective, it really takes 24mm to have full impact for wide angle work these days. An all-in-one lens has to take you from useful wide angle to useful telephoto. 105mm at the telephoto end is starting to get into the detail isolation realm for close subjects. If you go much beyond 105mm, though, the lens itself starts to get a bit long physically, and I think you're just better off getting a dedicated telephoto of some sort (zoom or prime) to get closer.
So what does Nikon have for us? Well, DX users are in luck: the 16-85mm is not only a great lens optically, but it pretty much defines a very useful mid-range. Its only real drawback is the f/5.6 aperture at the long end, but that's the price you pay for convenient, light, and small. We don't really have a great f/2.8 DX candidate, though the 17-55mm comes close. It's just a little too little at each end. The Sigma and Tamron 17-50mm f/2.8 lenses, ditto, though the Sigma is a very fine lens for what it covers. The new Sigma 18-35mm f/1.8 looks very promising for this range, too.
FX users have the 24-120mm f/4. The 24-70mm f/2.8 is wimpy at the long end, and it's big, heavy, VR-less, and a host of other things that make it less the slam dunk than it at first looks.
The one good thing about mid-range zooms is this: if no one makes the one you really need, just buy three great primes. All you need for FX is a 24mm, 40/50mm, and 105mm (some might prefer an 85mm if they've got other long telephoto options). Not as convenient maybe, but optically better. Realistically, you probably don't use all the focal lengths of your mid-range zoom, anyway. DX users have less luck here, as they don't have a 16mm prime available or anything that's even reasonably close. But what I'd do is use the 12-24mm, 35mm f/1.8, and 60mm Tamron f/2 as my three "primes."
The thing that's important to realize in these last examples is this: you can build a small, relatively convenient three-lens kit that gives you more performance in most aspects (low light, image quality, focus choices, etc.). The "convenience" you lose by not using a mid-range zoom instead is simple: you have to change lenses from time to time, and you need to move your feet. That really doesn't sound all that inconvenient to me, especially since I'm moving my feet already even if I'm using a zoom.