The EF70-200/4L is one of Canon's least expensive "L" series lenses. Using both fluorite and low dispersion glass optics, the lens is very sharp though out the zoom range and maintains a constant f4 maximum aperture. It is supplied with a lens hood and soft case, but does not come with a tripod mount (one is available). I owned and used this lens and I was impressed with its optical quality.
The lenses it competes most with are probably the EF75-210/3.5-4.5 (no longer in production), the EF 70-200/2.8L IS USM and the EF 70-200/2.8L USM , although the Canon EF 70-300/4-5.6 IS USM, the EF 70-300 DO IS USM , and the EF 100-300/4.5-5.6 USM also cover a similar range of focal lengths.
The advantage of the 70-200/4L over the 70-200/2.8L (IS) is that it is smaller, lighter and significantly cheaper (less than 1/2 to 1/3 the cost). Optical quality is, however, at least as good (some suggest it's better but the difference, if any, is small). The f2.8 lens not only has an intrinsic 1 stop speed advantage, but the IS gives an additional 2-3 stops of "hand holdability", so despite it's larger size and weight (and cost!), if you're handholding the lens in low light, the 70-200/2.8L IS USM gives you at least 3, maybe 4 stops advantage as far as camera shake is concerned.
Canon also have an Image Stabilized version of the 70-200/4L lens, so you can get the smaller size and weight of the f4 version, along with an IS system that's at least as good (as (and possibly better than) that of the 70-200/2.8L IS, Canon say it's good for up to 4 stops of added stability. Additionally the optics of the lens have been somewhat improved over those of the non-IS version making it an even sharper lens! The downside is that these changes have added around $400 to the cost of the lens, but if you want a lens in this focal length range with state-of-the-art (2008) Image Stabilization and you don't want the size and weight of the f2.8 version, the EF 70-200/4L IS USM is the lens to buy.
Both the f4 and f2.8 versions accept the Canon 1.4x and 2x TCs and both will provide full AF operation on any EOS body (film or digital) with the 1.4x TC. With a 2x TC the f4 lenses need an EOS 1D(s) series DSLR or an EOS-3 or EOS-1v film body to autofocus since the effective maximum aperture drops to f8.
The f2.8 lens comes with a tripod collar, while it is an extra for the f4 lenses. However if you have a 300/4L (non-IS), the same tripod collar will fit both lenses. If you have to buy one, Canon make two. One in black (originally intended for the 80-200/2.8L) and one in white (originally intended for the 300/4L). For some reason the black one is cheaper, so if you don't mind the color clash, you can save a few dollars. I find the tripod collar very useful indeed. The lens is light enough that you don't really NEED one, but in my opinion it makes the lens much nicer to use.
Unfortunately I wrote the original version of this review shortly after the lens was released in 1999 and for some reason I no longer recall I didn't include any test shots (it was before the days of digital SLRs and possibly before I owned a high resolution side scanner!). I do know that the images I got from this lens were very sharp, much sharper than those I was getting from a 75-300/4-5.6IS lens that I owned at the same time. Center sharpness and contrast were better and the edges of the image (full frame 35mm film) were sharper and showed lower chromatic aberration. I used it with a 1.4x Canon TC and the results were still good. I no longer own the lens, but if I can get hold of one for a day or two, I'll take some test shots and add them to this page.
However as some indicator of image quality, below is a comparison of the MTF plots for the EF 70-200/4L and the EF 100-300/4.5-5.6:
The plots are a little complex, showing lines for wide open and f8 at high and low spatial frequencies and for radial and tangential features. If you want to "decode" the plots, I explain them in more detail on my page about MTF Plots. However all you really need to know for an overall assessment of lens quality is that the higher the lines are, the better the image quality is, and as you can see, the lines for the 70-200 are significantly higher than those for the 100-300 and indicate a very high level of performance. The MTF plots for the 70-200/4L IS USM are very similar to those of the non-IS version.
If you can afford them, the 70-200/2.8L IS and non-IS are certainly alternative choices. I've reviewed the IS version in detail here - EF 70-200/2.8L IS USM Review
Another possible alternative to the 70-200/4L lenses is the EF 70-300 DO IS USM [see review], though it's more than twice the cost of the EF 70-200/4L without IS and almost $200 more than the EF 70-200/4L with IS. It is however quite a bit smaller and it does have image stabilization. One possible downside (besides the cost) is there's always a lingering question about diffractive optics. They they can certainly work very well indeed, they do still may show some artifacts under difficult lighting conditions.
The Canon EF 70-300/4-5.6 IS USM [see review] is also an alternative, possibly more so then the DO lens, since its price is much lower (around $550). It's sharper than the old EF75-300/4-5.6 IS USM and it covers more than the range of the 70-200/4L with Image Stabilization. So although it's 2/3 stop faster at 200mm (f4 vs f5), the 3 stop IS advantage means it can be handheld at speeds 2 1/3 stops lower. I think the new EF70-300/4-5.6 IS is a really nice lens and well worth consideration, especially if you tend to shoot wildlife or sports and need the extra telephoto reach. It loses out the the 70-200/4L lenses because focus is slower (it uses a micro USM, not a ring USM focusing motor), build quality is lower and it doesn't accept Canon TCs (though it does go to 300mm without a TC, so it has more reach then the 70-200 with a 1.4x anyway).
The EF 100-300/4.5-5.6 USM is the lowest cost option . The performance is reasonably good (better at the wide end of the range as can be seen from the MTF plot earlier on this page), but the 70-200/4L is definitely better with higher resolution, better contrast and better edge quality. Still, if you're looking for value, the 100-300 isn't a bad choice and it does have a real ring type USM focus motor, so focus is fast and silent.
The EF70-200/4L (IS) USM are among Canon's best lenses. If you need a lens that covers this range and can live without an f2.8 aperture, the f4 versions are the ones to get.