Yes, I would say that we definitely feel differently about Claudius after this point (at least I do). The main reason is that before this point in the play we've mostly seen two views of Claudius. We've seen his glittering public face, and we've seen Hamlet's judgmental views.

This scene gives us a third view: his own, when he's feeling guilty. Rather than justifying his crime, he compares it to Cain's murder of Abel, the first and darkest fratricide (brother-killing) in human history. He may be just feeling this way right now, but at the moment, he feels like his crime is one of the worst ever committed.

Greg