This is the first review I'm writing in this website so far, so please, don't judge my grammar.
One Piece is the best-selling manga series in all history. I'm not the kind of people who care about "the more people read something, the better it is", but this fact at least shows us this manga is worth some shit.
Yes, it really is.
One Piece is a part of the team of the successful shonens of the third millenium, amongst Naruto, Bleach and currently Fairy Tail and Toriko, now that Naruto is finished. Nevertheless, One Piece is someway different from them. But why?
First of all, there's a question in a need to be answered: what makes a good shonen? I think most people would answered "comedy, adventure and action". One Piece definitively has it. The amount of characters in the story makes it stand in a rather unique ground. Every fighter have different abilities, different weaknesses. And the comic situations Eiichiro Oda create are just hilarious. But the real thing that makes One Piece unique among the others long-running shonens is: It is not just one story. Every arc is different, each one has a specific story to tell, a specific pack of characters to present, all of them with its exquisite characteristics and motivations. The Alabasta arc is completely different from the CP9 arc, which is completely different from the Marineford arc (just to make some examples).
But it is the time when I come to talk something about the story. Not too much, just a preamble.
One Piece tells the story of a person named Monkey D. Luffy. He is a good fellow who wants to be a pirate. But not the usual kind of pirate, the ones who steal, put some homes on fire and murder. He wants to be a pirate to make a really good group of friends, have fun and kick some asses. He is one of the most easygoing people you will ever find in a fictional story. He really doesn't care about things most people would complain a lot. And he is completely honest; he always tells the truth, even when he lies (paraphrasing Scarface). He's got his first crew member in the beginning chapters: Roronoa Zoro, a swordsman who uses three swords that has a great ambition: to be the greatest swordsman in the world, and his man after became Luffy's right arm. The other members of the Straw Hat Pirates appeared after, and most of them didn't really liked Luffy at first, but then they became fond of his unique personality.
The last thing I want to talk about is the art. This is quite a contentious subject, for I know some people who like to criticize it. I somehow understand why they complain about, but I don't agree with them. It is said that the characters of One Piece are not well drawn. This is mainly because One Piece doesn't have the characteristic design of a manga, with the tram-sized eyes and all that stuff. But all the places are magnifically depicted: the sort of details in the sceneries is just amazing. And it makes me really like it.
Overall, One Piece is the best shonen I read so far. I'm not a real fan of this genre, but this story captivated me.