Probably the best DLC out of all of them, since the water mechanic changes how you play, by making you think before going in a certain direction because of oxygen.
New mobs and items are cool, although out of all the bosses in the game which go invincible for a bit, this one feels the most cheap and drags out the boss fight, since all it needs to do is swim off the platform you fight it on.
I wouldn't recommend buying any of the DLC by themselves, so if you want this and haven't gotten the base game yet, just buy the ultimate edition, even still If I had to pick one of them to buy separately, it would be this one.