Revised:

The mongo/options package uses chained-setters for constructing options. But types referenced by mongo/options, such as WriteConcern, ReadConcern, etc., are constructed with functional options style. Mixing styles confuses users and could be revised/replaced for consistency.

Additionally, some types are defined within mongo/options (such as Credential, Collation, etc.) but others have their own package (e.g. readpref.ReadPref, etc.). There is no obvious guide for what to expect to find where.

Original:

specifying writeconcern is difficult and confusing, and doesn't conform with the idiom established for options in the driver. It should be specifiable, perhaps with its own options type.