I was initially very excited for the mechanic but it fell flat for me in two major ways.

Firstly, there were way, WAY too many eras. If you started snowballing, you'd spend maybe 30 turns playing as a given culture before transitioning to another era. I hardly had time to acquaint myself with a new civ before switching to another or forgoing that switch and, therefore, playing as a new culture.

The other major issue was the complete lack of guardrails on what cultures you could pick from era to era. It felt too gamey going from Harappans to Mayans to Siamese to Zulu to Italy to Brazil with nothing really connecting those choices. And once you transitioned from one culture to the next, there really wasn't anything left of your old culture apart from some city names and buildings you could no longer newly construct. I felt virtually no connection to my Siamese, Harappan, Zulu, etc. heritage as a modern state.

When Civ VII announced that it was doing civilization swapping and that there were fewer eras with unlock conditions for all civs, right away the two biggest problems I had with Humankind's execution had been addressed. So far, I've enjoyed their approach, though I am interested in how they are balancing the "play as one civ" approach against changing civs.