No longer using Arch, but I can tell you what I liked about it:
it basically only does what you explicitly tell it to, making the setup very flexible. There’s no stuff the OS hides behind its own tools really (resulting in little to none “DO NOT EDIT THIS FILE” situations).
It is very up to date and the rolling release generally works well, there’s no pain with changing releases or anything.
The package manager, including creating your own packages, is dead easy and fast. Caveat is that once you look deeper into it, it gets more complex as you need to keep a container for clean building around. Still, with the right tooling, it’s very manageable.
As already mentioned, the documentation is very good.
Packages are very close to upstream, in most cases just being something like “./configure; make; make install”.