It uses all the cool features of the kernel. It's configured with text files, and has an override system that works great with the Linux filesystem layout and package manager -- much better than SysV init, by the way. And it handles a lot of little annoyances that have long been a thorn in an admin's/user's side on Linux.
I'd argue the better parts of systemd (it's not all bad but there's a lot of low-hanging fruit for all of us to gripe and bicker about) are the imaginings that came from launchd. That for sure was more UNIX centric than "linux" in particular.
You're right that the criticism "just become windows" seems weird - if anything else one should just say "get a mac" since that's where a lot of the launchd ideas originated.
For instance it's very reliant on cgroups, a Linux-only feature. The main project rejects even trying to be portable. This ensures there's no such thing as accounting for that some feature might not work on FreeBSD, because the project just clearly states that it won't be a thing on *BSD.