I have played one game nearly to completion (prince level - slug speed - no other mods) and:
- liked liked the tech & civic trees
- liked the inclusion of new units, buildings and merchant district
- but noticed I had no need for neighborhoods as I easily had 15 and 20 housing without them
- and didn't need so much housing anyway as even after the industrial revolution and after researching all growth bonuses my cities almost stopped growing after reaching a population of 10 (for instance even with a food surplus of 100 it would take about 100 turns to to grow from 13 to 14)
- had so many amenities thanks to buildings that luxury resources didn't matter much and the lack of them certainly not a constraint. Entertainment districts were useless.
- wasn't able to understand how training grounds really work as I never saw where and when the combat bonus shows up and is applied.
- and finally I would suggest some mechanic making early expansion more problematic, like having -1 housing and/or -1 amenity and/or -1 gold or whatever for each city with a cumulative effect within 1000 tiles (the way regional bonuses work for some buildings). Those penalties could maybe be lifted by buildings unlocked progressively through research.