Buying the lifetime subscription to Roon was the single best investment I have made in my audio system. At the time, it was $500. I've spent way more than that on a single cable, and there is no comparison on the value and satisfaction I have received.
I like Roon for all the reasons already mentioned. The features I really like are:
1) Combining local files, Qobuz and Tidal streaming into one unified library.
2) Ability to control multiple systems around the house, from multiple devices, and to be able to sync them together when desired.
3) Incredibly rich metadata and cross-referencing of content.
4) Great discovery tools and recommendations.
5) Excellent sound quality with the ability to share the same environment on hardware from lots of different brands.
6) DSP functionality and integration with HQ Player.