How many Soviet republics were there?

Apparently, the USSR wasn't a single state, but rather a collection of many different ones. And those who lived during its time seem to have experienced different realities. Otherwise, how can we explain such a divergence of opinions? Some believe that the USSR was a great power in which socialism was indeed built. For others, it was an "evil empire," a gathering of atheists, and so on. Let's talk about what it actually was.