So I've played around about an hour of the OpenDev so far and here are my immediate thoughts:

What I like:

1. You don't need to get every technology in an era to unlock later ones (e.g. don't need sailing immediately in the Ancient era, and can acquire ships in the next era and go back for sailing if/when needed)
2. Dead-end technologies! So many games don't go with dead-end techs quite enough. That being said... See my concern below.
3. The three paths at the bottom (science, civics, religion)
4. Shared city construction projects!

What I am concerned about:

1. Not quite enough technologies to my liking. I am the type of person to prefer having a ton of small technologies (little gained from them, at a lower cost) that build upon each other to make an immersive path of progression through the eras. Also, more flavour text is always fun :P
2. More specialized dead-end technologies. Having technologies that benefit certain environments over others but get locked out after a certain technology level (e.g. Ice fishing to add +1 food to neighboring ice shelves (I haven't seen enough yet to know if those are even ingame)).
3. Lack of branching. Having a more open concept for technological development (relates to point 1) gives the player more of an opportunity to develop how they want (e.g. certain techs that forcefully unlock civic trait slots, or certain religion tenets requiring certain technologies). This is simply a complaint about a lack of complexity. I was hoping for a Civilization++
4. As an extension of the other three, my concerns carry over to how the later eras are handled. Is there the same lack of depth in later eras as there is in the earlier eras? Does it get much better? Or only a little better?
5. The three paths at the bottom... I would like to see an espionage and space projects branch at the bottom. Espionage has already been handled by other games from Amplitude so until there is something to go upon, I'll leave that one be.
6. As for the space projects, I would like it to be an extension of the science tree (i.e. develop unique technologies specific for space that may or may not tie into points 1-3) An example would be researching Advanced Rocketry under the science tree then having specific engine qualities researched under the space projects (with maybe certain techs required to advance the quality of engine). Additionally, having certain "researches" locked behind projects being completed by cities (under shared constructions since it is more of a global/national effort). Having events/techs/projects related to colonization of other planetary bodies and exploitation of the solar system's resources would be awesome!
7. On the note about resources, I'm wondering if a climate change and resource shortage mechanic will be added for the later eras (e.g. oil running out, old iron deposits requiring more advanced technology to continue mining, organic resources dying out due to climate change, space projects supplementing resource supplies, etc.)

So that is my first impressions of Humankind specifically for the technologies and eras portion. I may have more to add the more I play, but for now I think this is good enough to comment upon for now.

EDIT: I feel this is specific enough to warrant its own thread, moderators or developers please let me know if you want me to post this under the general "First Impressions" thread.