There's a lot of stuff to do, even after beating the game and it never gets boring. Here's some of the stuff you can do in DQIX:
-Quests (Obviously. There are 180 quests.)
-RPG Fighting Style (Like Final Fantasy.)
-Wi-fi (You can play with your friends!)
-Customize your character (There is a whole bunch of armour and weapons and different things that you can equip your characters with.)
-Treasure Maps (After finishing a certain quest you can start collecting treasure maps. In the entire game there are thousands upon thousands that can be collected.)And there's more than that. I heart this game.