Generally I see a few:

• People wanting the highly deterministic, but slower behavior of the rc scripts.
• People liking the fact that the rc startup was generally almost entirely defined in plain script files
• Some folks criticizing certain opinionated things in systemd, as systemd delves deeper into things like capabilities and users.
• Systemd can sometimes be a bit weird about how it does/does not capture stdout/stderr as one might guess in some situations.
• Some folks not liking the journald angle of binary-only files

Mainly the last point is the only one I personally find potentially aggravating, but since I never really am in a broken system without journalctl I'm not too bothered by it. I have saved myself some effort thanks to systemd including stuff that the daemons used to provide for themselves.

I'm more frustrated with GNOME devs sabotaging Wayland.

So people hate on systemd because they interpret it as an init system thats gone too far and has thus violated the unix principle. in reality systemd is an entire suite of tools based around a very feature rich and robust service management suite that also includes an init system. there is something to be said about the Linux ecosystem's reliance on systemd, but there are no comparable tools. this is why Arch uses systemd. if you dont want to use systemd, you can use distros like Arco Linux; however currently Gnome no longer works on Arco