I've used it just a bit. AFAICT Shepherd is a fairly minimal dependency graph.

It's not comprehensive - in Guix there are services that exist above and below Shepherd and you can't define ordering dependencies between these (ex: a shepherd service can't depend on a mount (above shepherd), or an inetd service (below shepherd) on a database). I'm not sure that's a huge problem in practice.

Shepherd process stdout/stderr are sent to syslog. Shepherd automatically restarts services if they fail but not forever, and the retry behavior isn't configurable ATM.

The last complaint seems feasible to address have you thought of adding an issue?

Guix is a weird little behemoth of a distribution, that allows you to install different versions of different packages at the same time which then builds your effective file system on the fly. That being said, as mad as this sounds, I've heard people are having a lot of fun with it too, so apparently it's also manageable.

Guix is for you if you want to run old software on a discontinued software stack simultaneously with a modern system.

That makes it immune to dependency hell; there are no two packages you can't have at the same time due to dependency version conflicts.

The big wins for me though are: having all my system configuration in a small set of versionable text files (rather than gigabytes of mutable state), and being able to attach dependencies to the scripts that require them rather than to the system they're expected to be run on.

(I use NixOS, but it's the same concept)

Couldn't you have just looked into a little bit instead of saying you know nothing about it? It's a distro with functional package management. https://www.gnu.org/software/guix/