Silconera apparently has access to a leaked script for Dead Space 3, which has uncovered some interesting details regarding some new mechanics for the as yet unannounced sequel. Beware all ye who enter, this is 'slight spoiler' territory...
According to Siliconera's 'leak', Issac has changed and has a split personality which manifests itself in the form of a "Shadow Issac which will interact with you and taunt you throughout the game.
Despite being a little disappointed with the action turn Dead Space 2 took, I like the sound of this development. Hopefully "Shadow Issac is more than a visual, story-telling gimmick and actually has some impact on how the game is played. I think there could be some pretty slick ways to integrate a "shadow" into the general mechanics.
Isaac Clarke, You’ve Changed In Dead Space 3 [Siliconera]