What can I say? you go into it a noob and come out of it a pro, the tutorials are informative, the monsters are epic, the armors and weapons are amazing.
Never can get bored with the offline quests and then the huge amount of online quests, not to mention event items! Now how could you say no to that? Almost a MMO in fact Monster Hunter is in its own category.
In Summary PURE AWESOMENESS