Whenever I think of a raid, I always think back to Tower of Orthanc in LotRO... Strong difficulty progression centered on skill, weekly raid progression lock which makes you challenge the whole thing from the start each week but has specifically zoned sections you can tackle one night at a time and each section can take an hour or two with difficult trash and harder bosses. The "raids" we have currently feel more like small skirmishes to me and lack the grand scale that the term "raid" invokes in my mind.