Interestingly enough, when the schools in my locale started talking about Common Core, I decided to look it up. I found that one or more states had published complete curriculum guides written around CC, and since I like math, I looked through the math curricula.

My impression is that the CC curriculum (neglecting variations that I haven't seen) is so ostentatiously mainstream, that I can't fathom how it became controversial, except that people mistakenly associate it with standardized testing.