Well, just my two cents after going after 20-smth pages of mainly outrage (tough also some calls to calm, which I like).
Personally, i think the outrage for some may be justified, as it impacts the may way they see the civ experience, but it can't be hardly generalyzed.
I myself started in Civ I and Civ II leading customised Civs, terefore I started to be annoyed with the addition of "uniques" that forced me to use historical civilizations, breaking my own "build YOUR empire" experience. Uniques were nevertheless interesting gameplay-wise and for replayability, so I eventually started to adapt to them (still being slighty annoyed by things like Civ VI not allowing you to change the Leader name).
I see claims on civ "historicity" being broken by evolution choice exaggerated. There are many reasons pointed out, like leading modern era civs from the start of the game, or no having suitable succesorss. Regarding this last, bear in mind this won't hapen only for pre-colonization civs, which such an anglo-saxon centered game as it is, I could even imagine not having suitable successors for i.e. Exploration Spain: bleak choices to a modern Italy -or France

- , if you chose a mediterranian path, or having to become a "modern" South American state that actually independised from them (Portugal becoming Brazil is still more reasonable due all the monarchi changes, but still a similar thing to consider). The Netherlands might be a similar case, being forced to become Britain or Germany. It will be annoying at first. Yes, but I find it hardly disqualifing, more if some mechanics are put in place to manage the evolution choice.
A consideration regarding what is said aboutn immersion, as
@Republic of San Montuoso reminded
some posts before me: civilization switch ties into the crisis/era change mechanic which is a whole discussion apart an we may like or not, but it is probably the core change for this iteration (just to provide a preview of my impressions: it is bold and risky indeed, and a bit gamey, but I find it has a reasonable historical basis, and splitting the game in three games may indeed allow for better gameplay, so I'm excited to test it. But I would lie if I say I'm fullly confident and not worried about the final implementation - specially after some of the civ VI flaws. Still, I think its the developer right to test this new path and no, it's not doing something completely different)
And a final point of my own, gameplay wise I'll say if we isolate a feature of "play without unique options while your oponents have nice things to do", I would hardly consider this something many would say this like. Note that I underestand, strategy wise the "I have to endure this until my uniques come into place and then I turn the tables", but I feel that, on a grand-scale game of all the eras, this led to not completely satisfying situation as it really was difficult to find the sweet spot were your late unique might actually made a diference (as really the power difference where the unique might turn the tables was probably a narrow band, and you could either reach your unique era in a position either too good you could win without the unique, or too bad you would lose nevertheles). This strategic choice may be still be made in eras (early antique/exploration/modern vs late antique/exploration/modern uniques), but having that in a more limited timeframe will probably help not deviating too much.
Well, enough written so far, and too much to read still as I'm late to the party, Keep enjoying the discusion, don't get to heted up, and give some margin to hope

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