Well judging by the current situation and countless of story elements not yet resolved I guess the story is still far from the end. This series may go on for 7 more years.
Luffy still has to find three or two more crews
Luffy might face the three surpreme admirals.
Donflamigo is starting a new pirate age
Usopp wants to go to Elubaf
They are going to Fishman island.
There are two Shichibukai not yet seen
They might bump into Blackbeard again
They are still in the frist half of the Grandline
They may visit Maryjoa
There are ancient weapons not yet metioned
Luffy need to meet Shanks
Luffy need to fight Whitebeard.
There is a war coming, Luffy might get stuck in it.
There is a situation with Luffy's grandfather
Oda might throw in new islands for Luffy to visit, and may add new story elements.