Looking forward to your impressions of R&C when you peel your eyes away from SF25! and yeah those SF art books are amazing, I buy all the updates even though they're fairly similar lol love that Udon translated these with all the designer's notes intact and wish they'd do the same for the old Capcom Design Work books
So I've took time to go throught Art of Ratchet, and I'm mixed.
On one hand, it's massive and over all a very good quality of print, layout (sometimes old art cut from paper and made like a collage on the pages) and it's well commented enough (not super insightful but every pages as a few lines of explanation about what is displayed and sometimes design/art notes, so I can't complain). It also has a few pages, apparently exclusives never seen/shown before artworks of two of their project transitioning from Spyro to Ratchet, the fist, Girl with a Stick, a plateformer looking strangely like Jak & Daxter, and Madi, a game where you would capture and train and grow beast, like pokemon but with the insomniac design. So that's, short but brillant (because I have NEVER heard of these). It's also very generous in real wip concepts, it's not only marketing ready level of concepts, so that's also cool, a lot of sketches.
The problem comes from the amount of games it has to cover. I mean, they did like 4 Ratchet on PS2, 5 or 6 on the PS3 and the PS4 reboot... That's obviously too much to fit into 248 pages. The book takes you along the creation process for characters, weapons, levels, ideas, and then go back to each episodes but there are only a few pages per episodes at best.
I think it does a great job at celebrating R&C as a whole, and especially Insomniac trademark monster design (tons of super dynamic mean but goofy cartoon looking creatures) but it might fall short on specifics if you are very into a specific episode or even planets arts. It's very much a focus on character design rather than level or world design, for the better or the worse, depending on your expectations.