In a thread on the
Batman: Arkham City web site Sefton Hill, Rocksteay Game Director, wrote an update on the structure of the game. Here is a couple of excerpts from it.
Batman: Arkham City's story mode was designed to be story driven while remaining open world as we felt there was a really interesting space in between the two types of play. There is a main storyline which will take around 12-15 hours to complete, but this is less than half of the game.
In addition to this there are the new Arkham City Missions. These tell the story of what happens when Gotham’s most notorious super villains are locked up together. These run concurrently to the main story and can be tackled whenever you find them in the city streets. Some of my favourite moments are in these missions, including tracking down a deranged serial killer, solving a murder mystery, forming an alliance with a one-time villain and confronting the Riddler as he attempts to prove once and for all he is better than Batman.
Then of course there are the riddles and secrets to solve. We’ve had great fun adding these to streets of Arkham City. Our goal was always to create the most interesting and richly detailed open world game ever, and these make it rewarding to explore every square inch of the city. And Riddler has definitely raised his game this time. It won’t just be a simple case of finding the secrets. Nearly every secret requires you to use your gadgets in inventive and interesting ways.
Completing all of these will take around another 12-15 hours of play bringing the story mode time up to around 25-30 hours.
He also made mention that they are working hard to "polish" the game up.
For the full letter go to the link below.
Batman: Arkham City comes out October 18, 2011
Thanks to Lokisilvertongue