Unusual, but that's what makes it memorable.
When an anime or manga hears the mention of One Piece, odds are that they will be dismissive of it. It has a lot of things working against it: length, unusual art style, the infamous 4Kids dub, slow English release schedule, and so forth, but to completely ignore this work, very popular the world over and often praised as the spiritual successor to Akira Toriyama's Dragon Ball, would be a grave, grave mistake.
In a world primarily almost completely covered by ocean, a carefree teenage boy by the name of Monkey D. Luffy leaves his small hometown island in order to become a pirate and find the mysterious treasure "One Piece", left behind by the legendary pirate Gold Roger. During the course of his journey he assembles a crew called the Straw Hat Pirates, named after the straw hat that Luffy wears, and they travel across the treacherous waters of the Grand Line in search of Raftel, the hidden island where One Piece is supposedly kept. Along the way, they must not only deal with rival pirate crews, but also the machinations and conspiracies of the ominous World Government. While at first the story mainly consists of the crew traveling from one island to the next, an overarching storyline begins to emerge, dealing with the mysteries of their world and the balance of power between the World Government and the world's strongest pirate crews.
What most people will probably notice right off the bat is the unusual art style and character design. The art is very dynamic has extensive use of crosshatching and straight lines, resulting in some very exotic and impressively detailed backgrounds. All of the characters have their own memorable quirks and powers, ranging from the mundane to the truly bizarre. Half the fun is seeing what bizarre ideas and locations Eiichiro Oda will pull out of his brain.
That's not to say that this manga doesn't have its downsides. The author acknowledges that pacing is not always his strong suit. Some of the longer story arcs may start to drag on, and sometimes the story takes too long to answer certain questions. Also, some of the humor comes off as a bit stale since Oda rarely shakes up how the Straw Hats interact with each other, and after five hundred chapters, he's very set in his ways. And with such a large cast, some favorites inevitably end up shunted to the side to make way for new ones.
A recommended story.