Epic in general when youre wondering how fast time passes while playing the game!

Some main reasons for that phenomenon in my opinion:
- haunting story
- if you can follow the feelings of characters (RPG's)
- no loose of action - keep a certain tension
- sudden changes in story
- long-time motivation
- good character development
- rewards in general
- emphasizing exploration and discovery
- social interaction (online)
- ...

Final Fantasy X is an epic game!!! (: