How good is OSM data?
This is difficult to answer with a simple answer, but “good” should be a starting point. OSM data is created by local communities made up of individual mappers so their activity level often dictates the quality of the map. Also, in some regions, open government data is available to mappers for improving OSM.
Nonetheless, as OSM compares to the traditional map provider data, and OSM is now often as good or better as what is commercially available. This is evidenced by increased government and corporate usage and contribution.
There is one thing for certain about OSM; it is constantly improving in all regions.
Links below demonstrate some of the statistics that are relevant to make a comparison with third party data:
More research about OpenStreetMap, including many papers on data quality, can be found here:
There are a number of quality assurance tools here https://wiki.openstreetmap.org/wiki/Quality_assurance