followed the next waypoint or is it the next man. waypoint?
Technically, the next waypoint, mandatory or not. However, in some places (especially intl borders in south Asia and transitions to Oceanic controllers other than on NAT tracks), the controller will ask for different info. Commonly, there are specific waypoints on specific routes for which the controller wants your ETA.
Until you get used to the specific areas and their individual requirements, just follow the guidelines on the various charts.