I can see how people might be a little disappointed with the books if they were getting them looking for a ton of novel information that they couldn't get elsewhere.
I find the book valuable because it offers a one-stop-shop reference guide to basic gymnastics skills that you can take with you to the gym. I'm sure for each of the other books it'll be the same. The fact that there are a number of books doesn't surprise me because of the sheer volume and diversity of gymnastics training. It is true however that you can find pretty much all or most of the information for free elsewhere on the internet, including his own site.
Also, I like the compartmentalization of the books because I'll only pay for what I can do. I'm realistic that if I want to work heavily on both oly lifting and gymnastics, I may never really have any use for the advanced ring book or the dynamic book -- I probably will just never get to the skill level necessary for those volumes.