I don't watch any "Linux vet YouTubers" so I have no clue what they may be experiencing and running into, but I've been running it daily since alpha, and it's been rock solid. I've had a couple times where the Nvidia driver crashed that could have been caused by cosmic, but I didn't verify. Though both times I was messing with OBS and a virtual second display.

I don't like the file manager, the dock/panel are not as customizable as I wish, it'll glitch after running updates sometimes but a restart of cosmic fixes that. I was never a fan of tiling windows but with cosmic I use it daily on some workspaces.

There aren't a lot of applets yet, but I like these: package updater, privacy indicator, nitrate, minimon.

I wish I could have expanded ungrouped tabs in the app tray instead of a grouped icon, definitely my biggest annoyance. Otherwise I absolutely love cosmic. I've stopped using gnome after gnome shell, and it's never won me back, kde always felt like a side project just to get it to look how I wanted. Cinnamon is my second choice if Cosmic isn't available, but I really like Cosmic.