Snow Leopard was nine years ago to be fair. The UI/UX of Linux has come a long way since then, but the UI/UX could be optimized further. What is wrong with it?
To cover the common issues first: WiFi - Was an issue, but hasn't been on my machines at least six years. Sleep - Was an issue, but hasn't been on my machines at least four years. I've had this machine up to 60 day uptime, so 50+ sleeps, only restarting for the kernel update for example. HiDPI - Still an issue, but the apologist says "It was new tech! Just like the other two." Progress is being made, but it will be a while until seamless.
Due to my familiarity (with all three OSs) my UI/UX views may be incorrect for new users. I don't want a flame war. I want to know what else needs to be done in Ubuntu 18.04 GNOME and/or Mint/MATE. I'll file issues, create bug reports, and perhaps fix some things myself. It's easier to see this forest from another forest.
Edit: Further down the comments I found "Bluetooth" I'm going to look into it.