The idea of a centralized grammatically-accessible configuration store was a good idea (albeit this isn't want the registry was "for" originally-- it was just a file-type registry originally). GConf was a similar idea.
Devs misusing the registry to store opaque binary values (especially gigantic ones), accessing it with too high a velocity, and having a less-than-stellar file format have hurt it, for sure. Having few good schema rules or APIs that limited arbitrary developer access didn't help either.