You can't compare it to Sailor Moon. For one thing, SM came first, and their target audience was totally different.
Card Captor Sakura was actually more of a subversion of the traditional magical girl themes. Before CCS, most magical girl shows were innocent kiddie fare, even by Japanese standards. CLAMP upped the ante by adding more mature themes, such as incest, generational romance, teenage pregnancy (guess how old Sakura's mom was when she had Sakura), lesbianism, gay, pedophilia, bestiality... hell, name it, there's probably an episode/chapter (it started out as a manga, after all) about it. It was popular enough to be an influence to all shows that came after it, such as Pretty Cure and Nanoha.