GUIX (and NixOS) are significantly different than other package managers. They get you declarative system configuration, immutable and reproducible builds.
Declarative config = entire system config specified in a single config file - all config that is normally scattered across different /etc files and other locations now goes into a single config file (which instructs the system to write those /etc files on install, so /etc is still used but there’s a single source for configuring all of it). All packages and package config, boot loader, systemd/init system config, networking, etc configured in one file. And all config is declarative, not imperative - eg, you tell the system what you want in your build, and the system handles how. In NixOS this all just a big JSON file, and GUIX it’s a Scheme data structure.
Immutable builds = any time you make a configuration change, an entire new system is built with the change incorporated, and the system updated to point at the new build. Prior system builds are retained unchanged, and you can rollback to them any time if needed, if your new one is broken in some way not caught by compiler. Since current and prior builds are immutable, you can be sure that if a prior build worked reliably, it will continue to do so in case you need to rollback to it. In NixOS, builds are stored in /nix and soft-linked as needed to /bin, /usr/bin/, etc. Not sure about the equivalent on GUIX but that’s the idea.
Reproducible builds = you can take your system configuration file and use it to install an identical system build on other hardware. Everything will be the same except different hardware drivers for different hardware. Reinstalling the same configuration on the same system with no hardware changes will result in an identical system build with the same checksum.
One thing this does is make rapidly experimenting with different system configs much more possible. There’s no penalty to experimentation and failure, you can’t brick your system. If you do, just rollback to the prior working config, only takes a few seconds. You can iterate through many different config ideas, testing them all, and optimizing it to your needs.
I spent the past spring/summer migrating to NixOS. There’s a learning curve, but now that I’ve gotten through most of it, I could never go back to a normal linux. GUIX/NixOS is really the right way to architect an OS, so much farther out of the tarpit than anything else I’ve seen.