"The latest chapter in the Assassin’s Creed saga also includes revolutionary gameplay, allowing players to manipulate the construct of Desmond’s memories and the Animus to decipher the mysteries of his past and gain insight into the future."
What exactly is meant by "manipulate the construct" is unknown now, but sounds like the most interesting nugget of information from the release. Expect more during this year's E3 for sure.
You can read the official press release for yourself.