One piece is great. And big. And huge. There are no other words for describing a work reaching the 1000 chapters goal, and being still far from being completed. But it's not only a matter of physical size. The astonishing thing about one piece is it being still fun and interesting after all this time. The merit goes to Oda, who uses the tradiitional formulas of battle manga but backs them up with a well-thought and coherent story and well designed characters that grow (especially Luffy) with time and with the experiences they make.
The whole manga is a hymn about freedom and following your dreams. I would not be surprised that in the end the "true treasure is the dream itself and the friends we make during our voyege". A theme already seen in other works, but in my opinion no work like One Piece makes it feel so real. There are also defects, too: in some arcs it becomes a little confusing, especially if you follow it week by week. But all in all it is an experience you should not miss if you are a manga lover like me.
I would like to share more, and going in detail about what I liked during all these years, but the review would grow so huge it would be a hadr work for me to write and for who's iterested to read. I can only add: have fun!