Deb's ex-fiance tried to kill her. Was she back to normal ? Nope. Dex killed his brother. Did he carry on as he always did ? Nope. Doakes knows that Dexter is not a normal human being. Does he ignore this ? Nope.
There was a lot of pain in the last season. A lot of things changed for the characters, and this season, they have to deal with it. Dexter killed his brother, and in doing so, caused (more) psychological problems. He is suffering a block, so he is unable to just go ahead and kill his victims anymore. He needs to deal with his problems and move on.
I like the fact that the characters in season 2 are in a different place than they were at the start of season 1. Life changes. Things are different. People deal with issues.
I look forward to watching the rest of this season.