What is the appeal of Monster Hunter games?

While researching good PSP games to play I found many posts about Monster Hunter Freedom Unite and other Monster Hunter games. They are beloved by the community but after doing some reading/watching it's not clear to me what the appeal is. I would appreciate if someone could tell what the goal is and what you love about the game. Apparently they are very long games (I think I read 100 hours or something along those lines) which is really great if I can get into a single game for that long. Thank you!