I get why they decided to do it this way. Mao Zhedong fighting Napoleon with war elephants in 1000BC was always a bit of a running joke in the old Civ games. So instead of playing a single civ from start to finish, Humankind has you switching to a different civ every time you advance to the next age.
The result is a complete sense of schizophrenia and alienation. You start as Egypt, then turn into Rome, then become England, Korea, then France. Meanwhile, they're all being led by the same blonde pale dude (your avatar), cosplaying and looking super out-of-place half the time. Your cities are still called Memphis, Thebes, etc. The architecture just bizarrely changes from Egyptian to Roman, then suddenly East Asian, then suddenly European again. There's absolutely no sense of consistency, theme, or ownership. Pretty soon, you're just minmaxing the abstract game mechanics, getting your numbers up, and stomping the other nondescript, schizophrenic cosplayers without any feeling of leading a people through history.
Meanwhile, the same thing is happening with your neighbors: you start next to Harrappans (ancient Indians), so you've gotten used to thinking of them as Indians. You're intuitively expecting an Indian culture to be developing next to you. But now they're Celts. And now they're suddenly something else. The idiot on the other side is Mycenean-Hun-Polish-Aztec-Whateverthehell. You feel no sense of relatability or connection to the other civs, because you don't even know how you're supposed to visualize them in your head. Pretty soon, you're only killing them or ignoring them.
Ironically, this approach also gives you less, not more freedom. Want to play England? Nope, wait until the middle ages. Want to play Russia? Wait until the game is nearly over. On the highest difficulty settings, you also have to be mindful of the bonuses/abilities each civ gives you, which further restricts you to only a couple options that are actually viable in your situation.
On that note, Humankind also sacrificed one of the main things that gave the old Civ games so much of their personality - the cast of historical leaders. You won't get to feel that gravitas and weight of dealing with Alexander Macedon, Chingis Khan, or Lenin. Instead, the aforementioned schizophrenic, faceless cosplayers periodically disturb your minmaxing, forcing you to remember who the hell they're supposed to be during this particular five-minute interval.
This is 180 degrees from the incredibly diverse, flavorful factions in Endless Legend and Endless Space 2, where you really feel that you're playing a very distinct faction with its own special character and feeling, surrounded by other interesting people. Amplitude rejected one of the main things that made their games so good.
The aesthetics also rub me the wrong way, although I have the same complaint about Civ 6. The avatars are fidgeting and grimacing like BuzzFeed eunuchs, not world leaders. The art is happy-campy-colorful, which forms a surreal backdrop to the war, starvation, industrial pollution, and tyranny that is supposedly unfolding in front of you. The game seems to struggle to take itself seriously, which doesn't exactly help the player take it seriously.
The underlying mechanics are mostly very solid, Amplitude knows what they're doing as always. There's a well-made game somewhere underneath all that. Unfortunately, that's not enough to salvage a game devoid of any immersion or sense of investment.
I have to make this a thumbs down, because these problems can't be patched out or fixed with DLC. I'm a big respecter of Amplitude and it hurts like hell to criticize them, but Humankind doesn't live up to their previous games.
I apologize for being verbose.