It is difficult to sum up the story of a series with hundreds of episodes, TV specials and movies, so I'd rather just try to tell you what it is about and why it is so incredibly good.
The series starts off with a guy named Luffy whose ultimate goal it is to become the one and only "King of all Pirates" and to find the greatest treasure in the world. The first episodes introduce him and some characters and make a lovely start that is entertaining and makes one want more. On his way Luffy meets a lot of very interesting characters who become his crew members and friends - each of them with an intense and captivating background story. Every character in this series - be it friend or foe - is either adorable, tragic, despicable or interesting at the least... no boring characters anywhere. Later on in the series, important events and story twists are often visualized or supported by huge appearances in the fabulous and unreal environments that our crew travels. This is perfectly done and helps the already epic feel of the story. I have seen 150 episodes, four movies and two specials so far and there were moments that made me cry, laugh, think and re-watch some episodes (especially 85-90) at least 30 times. You might come to the false conclusion of having a kids show here due to the presentation, but that is definitely wrong. People sometimes say about a movie or series that it is "not a life changer, but entertaining". That is definitely not the case here! I know it sounds nerdy, but this series has broadened my horizon in many ways and I recommend anyone to take the admittedly long time to get into this epic adventure. The best way to do so will be to watch the fan-subs which are as close to the original as a non Japanese will get (explanations of puns and traditions). There are of course some filler episodes in a huge project like this which won't blow you away, but that is only natural with hundreds of episodes and helps developing the characters. This show is an easy 10/10