I usually play UN and CoM, leaning more toward CoM.
Problem I had with CoM was that I had too many slaves and not enough jobs so endgame I had a lot of planets with unhappiness due to unemployed pops.
I also wish there was a larger variety of endgame crises.
I don't know if I'm doing spycraft wrong but I only have one option to pick from, "Gather Intel" IIRC?
Lastly, I wish that I could build at least one type of megastructure. I see tech and buildings that mention "Dyson Sphere/Swarm (idr)" and "Orbital Rings" but I can't build any of those (AFAIK) so it's just teasing me.
Any good expansions that solve some (or all) of these problems?