YAS! An intelligent and meaningful weather system would add a TON to the lacking immersion.
I think having the zombies be randoly generated with varying health, damage, move speed and especally looks would add a ton. Killing zombies gets boring for me as its all the same exact clones over and over.
Like zombies have classes lets take the nurse zombie: looks are randomize but they stull have a nurse outfit or hat at least, health could be between say 80-150, damage between 10-20, move speed between 80%-120%, I mean if these were monsters in the normal sense then each of them being the same is fine, but since they were previously humans, they should have far more varied looks.
It does get better in later gamestages when some ferals that always run get mixed in with the normals.
I normally build a base underground as I see no reason at all to build on the surface right now. If npcs could move in but the base had to be on the surface i'd build one there then, but since nothing like that is ingame, underground it is. I do have my farm on ground level though but thats usually just a plot of dirt in the desert.
They tried the random looks thing a bit with the UMA zombies but the performance was so god awefully bad they had to scrap them for now. Even high end pcs would slow to a crawl if more than a few were on screen with the UMA ones.
Funny thing is, I really like 7dtd, I always come back to it after taking a break for a while. Its my most played game on steam with over 1350 hours. I may complain about some things, like in this post, but I still enjoy the game. I am really waiting for a17 since it seems like its going to feel like a entirely new game. I hope they stick with it, and don't decide to completly remake it all in a18 all over again.