There is one thing missing in the list of disappointments in the OP :
They had Sleepy Hollow in the game (complete with pumpkin scarecrows and the famous bridge from the short story) but didn't do anything with the location like having a mission where you either pretended to be the Headless Horseman to assassinate someone, or had to track down and kill someone who was using the legend as excuse to kill people. Even just some dialogue that people sometimes disappeared from the roads late at night or something would've been cool. Would've been a nice sidequest, and even better if it had been a Halloween themed DLC like Undead Nightmare from Red Dead or Nightmare in North Point from Sleeping Dogs. You could have met Ichabod Crane as a historical figure etc, and upon completing the DLC unlocked a Headless Horseman skin with ripped clothes and all that jazz. That would've been so cool.
Also, the final legendary ship battle was complete insanity, and that mission where you start off poisoned can go to hell.