When I read Races & Classes, we knew less about 4E. It was an awesome read for me then, there were so many ideas I liked and agreed to or found inspiring.
When I got World & Monsters, I knew a lot more about 4E. The information in W&M wasn't that fresh anymore to me, so it was "just" a good read for me. Still, I find the cosmology very inspiring, and when I think about what I want to do for 4E, I think about the contents of the W&M a lot more than I think about R&C.