It seems that the top of the booster fell off when the booster tipped over after a wave hit the droneship. Hopefully not typical.
The bottom portion (RP-1 tank), the landing legs, and the engines stayed on the ship. Octagrabber sustained some damage.
Photos from various Florida Spaceport photographers:
Videos from NSF Space Coast Live:
SpaceX had previously noted that newer boosters have an updated landing leg design with much better stability, which would have survived these rough seas.
Wonder if they duct tape a new aluminum façade to replace the missing lox tank, and mock it up in Cape Canaveral somewhere.
SpaceX VP of Launch has shared some details: https://nitter.net/turkeybeaver/status/1739640175183945860