Objectively, One Piece is not the best manga. It has it's own sets of problems such as the base structures of arcs being repeated and the characters not being developed. It has a problem killing off characters. The art is decent, not extremely good. However it is still one of the best manga to ever exist. One Piece fleshes out it's world beautifully, with each setting being unique and interesting. The world is alive and breathing and doesn't remain stagnant until the main protagonist does something. The main characters, the Straw Hats, are amazing characters. Seeing the unbreakable bond of trust between them never ceases to amaze me. They do not have drastic changes in character writing throughout the course of the story, because One Piece is an epic about how the Straw Hats are changing the world. In my personal experience, One Piece bought about a spark of adventure and exploration to me. It shows the world is a vast place, and is often beautiful but tragic. The world of One Piece is much darker than it appears to be. Every Straw Hat has their moment to shine and is well written. Often plot points from hundreds of chapters earlier are still bought upon to the current chapter. Seeing the Straw Hats grow from a crew weak and powerless to being one of the strongest crews is amazing. One Piece is often criticized of dragging along but the best flashback and depth of One Piece happened in the 967th chapter. The amount of work, dedication and passion Oda has put in One Piece is truly exceptional and shows at the climax of every arc. It has it's own themes of inherited will which are simply beautiful. No other series has ever reached the high that One Piece has. The Water 7 Arc, Marineford,Whole Cake Island and Wano Arcs are good enought to be shows rated at least a 9/10 individually. Oda loves fleshing out the world and it's wacky designs, it's creative powers and it has the most mysteries present in a series. To me, One Piece's journey is a magical one and the day that it ends will be a tragic one.