Sea of Thieves has three gameplay pillars:
The main game:
- Your main goal here is to become a Pirate Legend and reach end game activities. There are factions to join to level up in your quest to become Pirate Legend. Each of the factions has various mission types and goals. There is also an Athena faction (good) vs Reaper faction (evil). There is also an overall storyline and struggle of Athena vs Reaper in the main open world game.
- Various world events, like Skeleton Forts and Fleets, seasonal events, Sea of Thieves Adventures, Sea of Thieves Mysteries, one time story events, random world events, exploration, etc., etc.
- Guilds - Join player created guilds and level up your guild.
PvP Mode:
- Hourglass - Join Athena (good) or Reapers (evil), dive and battle it out in ship v ship combat. This replaced the old Sea Dogs Arena PvP mode.
Tall Tales:
- Gold Horder storyline (The 9 original Tall Tales)
- Flameheart storyline (2 additional Tall Tales and possibly continuing in Season 14)
- Pirates of the Caribbean storyline
- Secret of Monkey Island storyline
And they also constantly add new stuff to do with every season.
Last season they added the Skull of Siren Song voyage.
This is literally a recreation of the ending of POTC: Dead Man's Chest where everyone is competing to find a skull to turn it in (it sells for 50,000 gold so it's worth it).
You get the quest and you need to find a chest and then its key. Unlocking the chest gives you the skull. As soon as ANYONE picks up the chest, key, or skull they're visible to EVERYONE on the map and they have a giant blue beacon coming off their ship that can be seen from almost anywhere in the game.
It's so fun. I've had Galleons chasing brigs chasing sloops to get the stuff.