Here are the new fields for the series entity:

name (maps to series.name in SQL)
comment (maps to series.comment)
type (maps to series.type which joins on series_type.id to get series_type.name)
orderingattribute (maps to series.ordering_attribute which joins on link_attribute_type.id to get link_attribute_type.name)

Series also have aliases and annotations like other entities.

Here's the schema referenced above:
https://bitbucket.org/metabrainz/musicbrainz-server/src/schema-change-2014-05/admin/sql/updates/20140318-series.sql?at=schema-change-2014-05

Here's the mmd-schema changes:
https://github.com/mwiencek/mmd-schema/compare/master...series