There's an article about this in the latest issue of Edge. It mentions how they're replacing the composer from the previous games (he's working on the new Assassin's Creed, so that may be why), as well as the voices of Diana and 47. Though the part about Bateson not returning as 47 isn't a direct quote and the official response right now seems to be "no comment", so there may still be hope. I'm already annoyed by how they decided to replace the voice of Diana after three games.
47 will apparently be more agile in this game, and he'll actually be able to sneak this time, rather than just walk around like a robot. So that's nice. The all-seeing map is gone, and now there's going to be something akin to the detective mode in Arkham Asylum instead.
The game will have "smaller sandboxes" and a "checkpoint structure", but the article also mentions how there are going to be larger free-roaming levels, so I'm not sure how that's going to work with checkpoints. Freely walking around a huge level and experimenting was one of the best parts of the previous games.
Overall, I'm slightly worried that this is going to turn into another Splinter Cell: Conviction. Hopefully they'll manage to strike a balance between new and old.