Pretty much a perfect DLC. it expands upon the lore and story of the original game in a way which feels natural, and satisfying. Fleshing out characters, and even the backstory of the world itself. Every boss is great, and overall as an experience, it's must-play. It completes the game.

The downsides which keep it from a full 5-stars, are:

1) It lacks the intricate level-design that base-game has, being far more linear.

2) It is a tad on the short side. That doesn't make it bad, but there's DLC which has similar levels of quality while being a lot longer.