I feel like I need to split this up into two parts.

First the main game:
There is a reasonable amount of story here, I thought that it did finish in quite a short amount of time but the added extra side-quests type things managed to help bulk it out a bit. There are additions with the DLC for Harley's Revenge which is also quite short and playable in a sitting.
Is it a lot? Not as much as I thought - If the game is on sale, the campaign alone is worth the price tag. You get multiple characters, decent amount of Batman-ery.
What did bulk it out is my sense of completionism. Dear ******* lord. The Riddler can go to hell!

The Challenges:
The Collectibles, OK not too bad. They are do-able and can be found without the help of guides through being able to populate the map. What killed it is the Riddler Challenges in the extras, dear god. Some of those can go into a fiery pit of despair! If you hate yourself you'll try to 100% them with all the characters, it's driving me insane!
The fact that this game has a 100% stat on the menu is killing me! HELP! PLEASE!

TL;DR: Good Campaign - worth it, Insane Challenges 100% not worth it!

I feel like I need to split this up into two parts. First the main game: There is a reasonable amount of story here, I thought that it did finish in quite a short amount of time but the added extra side-quests type things managed to help bulk it out a bit. There are additions with the DLC for Harley's Revenge which is also quite short and playable in a sitting. Is it a lot? Not as much as I thought - If the game is on sale, the campaign alone is worth the price tag. You get multiple characters, decent amount of Batman-ery. What did bulk it out is my sense of completionism. Dear ******* lord. The Riddler can go to hell! The Challenges: The Collectibles, OK not too bad. They are do-able and can be found without the help of guides through being able to populate the map. What killed it is the Riddler Challenges in the extras, dear god. Some of those can go into a fiery pit of despair! If you hate yourself you'll try to 100% them with all the characters, it's driving me insane! The fact that this game has a 100% stat on the menu is killing me! HELP! PLEASE! TL;DR: Good Campaign - worth it, Insane Challenges 100% not worth it!