There are plenty of iconic manga and anime at this point and there will be more to come as manga and anime continue to expand. For every Dragon Ball or One Piece there are plenty of lesser known manga which is what makes me ask why series like DB and OP are so popular? There must be a quality that they have that puts them above other manga in terms of popularity.
Personally I don’t read or watch One Piece so I don’t know what qualities it possesses but for the Dragon Ball series it’s an interesting question. Looking at the success that the series has experienced it’s fair to say that a good story isn’t necessary for a manga to be successful especially when looking at DBZ. The story of DBZ wasn’t bad at all however, the formula for the Frieza saga was rinsed and repeated for the following storylines. It did provide memorable moments such as Gohan defeating cell and Goku turning into a super saiyan for the first time.
I wouldn’t say that memorable moments are what make a manga or anime popular, I don’t recall any particularly memorable moments in Yu-Gi-Oh! yet the success of the series speaks for itself. The same goes for Fairy Tail, if anything Fairy Tail isn’t even a good series but it still has many readers (myself included).
When looking at successful series, it easy to see that what makes one series popular won’t be what makes another series popular. In turn it makes it harder to find an answer to what makes a manga popular; a good story, memorable characters and moments are only pieces of the puzzle but not all of these things are necessary. It seems like whatever a manga does, it has to do well.
If there’s no definite answer then it must come down to the fans.