I agree. Used it for multiple projects already. As one of the main contributers to the parts library I especially like Horizon's parts pool concept for these reasons:
- the modularity (+inheritance) allows you to reuse a lot of existing stuff and change things in one place while affecting all
- the simple json format allows you to create parts/packages/etc from scripts very fast
- the package footprint editor is great and has generation scripts for a ton of existing packages (SOIC, QFN, etc.)
I heard it was planned to release a 1.0 on the next FOSDEM in january.
[1] - https://github.com/horizon-eda/horizon