He has some very useful information and is pretty "up on" a lot of cameras and lenses, since he has the means, and the "type of job" where buying and trying and using different camera gear is a part of the job. In recent years he's moved away from being all-Nikon, and has acquired Canon, Sony,Leica, and Fuji equipment, and has begun reporting on how he likes that stuff.
I think Rockwell has some good advice for people interested in practical picture-taking and hobby photography, and for people who want a strong, plain, simple opinion on equipment under consideration. Today's major corporate-type sites, like dPreview for one specific example, (dPreview is owned by Amazon.com) really tenderfoot around issues and problems with things under review. Ever since AMazon.com bought dPreview, their reviews have tended to gloss over issues or weaknesses with carefully-worded phrases, and an overall effort to mention-but-minimize weaknesses in products.
Just yesterday, I was going to tell a new potential buyer this bit of advice: Go to dPreview and carefully read the review of the Pentax K-30 and the Nikon D5200, and then note each instance of an "issue or problem", and then give each mention of an issue or problem about three times the weight in your mind as to how big a problem that issue is. Rockwell is not like dPreview; if something is stupidly designed, he states it that way.
On the other hand, Rockwell is tricky to use as a review source on some things because his reviews and comments are all mixed together over the span of years, and things can, and do change over time. At ONE TIME, the Nikon D70 was a great d-slr...today it's pretty lame by comparison. I used my D70 late last year...OMG...what a turd that thing is. But if you pull up a KR review of the D70, it's lauded pretty heavily. Same with his Nikon D40 reviews. And you know, for a time, the D40 WAS hot stuff! The old-mixed-with-new is one reason each new generation of zoom lenses is touted as, "The sharpest ___ to ___ lens ever!"
The one thing you will get from KR is an opinion. Clearly stated, no punches pulled, and I think that for the hobbyist and non-gearhead, his buying recommendations are usually pretty good; like what a competent,capable camera salesman would tell a customer. The more-advanced a shooter, the more-likely he will disagree with Rockwell, since Ken's buying advice is geared toward MAKING PICTURES, and less toward buying a war chest set of gear, which is what the majority of internet forum posters tend to favor. For example, KR (and Thom Hogan as well) both favor the Nikkor 16-35 f/4 VR OVER the 14-24mm f/2.8 for ACTUAL USE and CARRY; the 16-35 costs less,takes filters, is smaller and lighter, and has a wider and more-useful range of lengths; they prefer the 16-35 for most uses; on forums, that preference for the 16-35 over the 14-24/2.8 is regarded by buyers of the 14-24 as heresy, and so, people will bash him because he will buy and use lenses that they consider "inferior". I see that all the time here too.