One Piece vol. 7 continues the Don Krieg story arc started in vol. 5. This volume is notable for its revelation of Sanji's backstory, and why being a cook and not wasting food is so important to him. Without spoiling too much, I'll say this: if you've only seen the anime version (4Kids butchering or Japanese original), be prepared for something much more shocking. This isn't a rehash of Luffy's origin as depicted in the anime.
Unfortunately, the framing for this backstory is rather awkwardly stuffed into the middle of a fight scene, which is my main problem with the Don Krieg arc: talking. Characters stand around making statements about their dreams and powers before actually doing anything. Shonen action titles all suffer a bit from this, and its very noticible here. It's a little easier to swallow in graphic novel format; I can't imagine slogging through this on a monthly basis during the original magazine publication.
The volume is mostly three stars, but the inclusion of Sanji's backstory bumps it up to four. Keep on reading, the arc ends next volume.