Slow startup time, doesn’t honour system themes and big download sizes come to my mind.

snap backend is proprietary and controlled by canonical also people don’t like the slow start up times

There are better solutions for everything it does/tries to do:

• Flatpak for desktop applications
• docker/podman/LXC/… for server software
• apt/dnf/pacman/… for system utilities

It automatically updates the software you’ve installed, and there’s no way to turn that off. That’s why I personally hate it.

One thing really annoying for me, there’s only the 1 official “store” you can use and it doesn’t support ipv6.

https://wiki.ubuntu.com/IPv6 says it’s been available for apt since march 12th 2013.