First, this is definitely best enjoyed after the 2nd or 3rd island in the main game. This would feel pointless if you started the DLC after finishing the main story and already having a ton of endgame upgrades.

As a mid-game addition it works great. Really just another island with another type of fish and set of gear to use and it's more of the same as the main game which is great.

The DLC story I actually enjoyed more than most of the main games' side missions. It had a good set-up and did a good job of letting you uncover the mystery without spoon-feeding it to you. The main threat in this area was better than the monsters on the main islands too and had decent mechanics to combat it.

Short, sweet and more of the same Lovecraftian goodness.