Picking up from where vol. 5 left off, vol. 6 of One Piece finds the Staw Hat crew aboard the ocean restaurant Baratie, where Luffy has to work as a bus boy after injuring the head chef with a rogue cannonball.
Honestly, the Baratie arc is one of my least favorites, as there's not much variety in the scenery and the battles become very dragged out. However, vol. 6 contains a host of important plot points that are essential reading. Don Krieg, the villain of the arc, is introduced. He's one of the few villains who doesn't use devil fruit powers, and instead relies on technological weaponry. The other new pirate is "Hawk Eyes" Mihawk, one of the seven most powerful pirates on the ocean. His honour duel with Zoro is the centerpiece of the volume, and further develops Zoro's motivations while just being a really cool fight. Finally, during the chaos Nami steals the Merry Go (Going Merry) and takes off, setting up the next storyline in the saga. Oh yea and Sanji, the next Straw Hat crew, is also further spotlighted. There's a lot going on here, making vol. 6 worth picking up.