Let's see...

• Main character isn't even real, finds out he came from a dream world version of the past of the current world he's in
• A giant monster called Sin rampages and attacks various villages/cities and the people believe it is because of transgressions of the past
• Summoners are sent on a pilgrimage to become sacrifice for the people or Spira in order to temporarily sate Sin
• Technology of the past is largely abandoned because people believe it is responsible for the appearance of Sin
• At the end of the game Sin is revealed to be the father of the main character, which is strange because they both came from a dream version of Zanarkand
• Heavy emphasis on dreams being able to be manifested into reality?

This is what I can remember off the top of my head but I haven't played the game since I was 12...

Let's see...

• Main character isn't even real, finds out he came from a dream world version of the past of the current world he's in
• A giant monster called Sin rampages and attacks various villages/cities and the people believe it is because of transgressions of the past
• Summoners are sent on a pilgrimage to become sacrifice for the people or Spira in order to temporarily sate Sin
• Technology of the past is largely abandoned because people believe it is responsible for the appearance of Sin

This is what I can remember off the top of my head but I haven't played the game since I was 12...