I started the DLC right after I replayed the game about 2 months ago, but I put it off for a while because I got stumped in the Moonshine Mob boss fight (the third phase to be exact).
I decided to finish the whole thing in a sitting and what a ride this was.
Instead of just adding new boss fights (which is what might be expected from a DLC for a game like this), they went above and beyond that.
All bosses just ooze with creativity and style, be it in the small details in their expressions or how each boss fight has distinct phases very different from one another.
The addition of Ms. Chalice wasn't just for pure cosmetics, her new moves, the double jump, the invincible roll and the one-button parry have made the boss fights more fun and opened the way for more creative maneuvers.
The chess boss fights that relied solely on the parry are still one of my favorite parts in both the base game and the DLC.
I still don't appreciate the randomness that sometimes plague certain sections of the boss fights, as it makes reaching the final phase that much more frustrating, like the laser placement in the third phase of the Doggone Dogfight, though it was an awesome boss fights and I was really proud after beating the final phase (I had to turn my head 90 degrees).
The final boss is definitely the most challenging, and also the best-looking boss fight in all of Cuphead.