Some observations that I haven't read (enough of) yet:
- great works and great work slots (aside from the palace) are age-specific. In the stream, Ed had some codices in antiquity, but none of them (nor the slots from the library) made it into the exploration age. With religion being a focus of the 2nd age only, it seems likely that the same happens with relics and temple slots.
- we've been told that trade works differently in each age. We haven't seen any trade in the stream, right? I also didn't catch any merchant unit in the production overviews, but I also haven't looked specifically for them.
- the fact that leader and civ traits give you a respective attribute point per age, and the bonuses down the tree seem quite strong, means some synergies might arise simply from having a good trait fit between your leader and all your civs.
- the meta-progress per leader exists as a gameplay feature that results in at least one unique legacy per age. Isabella's exploration legacy didn't seem like a no-brainer OP choice. I really like that: not just cosmetics, but also not something that you absolutely need to have to stay competitive. Curious how hard they are to unlock. Finish all trees with the leader?
- I wonder how many "your legacy goal works different" civs à la Mongols we'll see in the base game and early expansions. This has huge potential for different play styles.
- I hope that FXS manages to find 2-3 legacy goals per age per type to have some more variety at some point (maybe as focus of the first major expansion). It would be "fun" to not know what's waiting for you in the next age in a way.
- events that don't trigger just because the conditions are fulfilled is a godsend.