Eric's arc this season has been admitting to himself he does care about humans and in fact still has what he considers human emotions. We've seen him struggle with feeling more for Sookie than he likes to admit and we've seen him follow a need for revenge that often puts him at odds with the people he cares about, from Sookie to Pam. In the finale, he adds Godric to the list of people he's willing to push aside to get his perfect revenge.
It's not entirely clear whether Godric is a manifestation of Eric's conscience talking to him or an actual Ghost of Godric, but in either case, he represents a side of Eric the vampire doesn't like to admit to, a side that cares about the ethics of his actions and the big picture of where he fits in the world. These are the very questions Godric struggled with and eventually decided to end his existence over. From Eric's response to Godric this episode, it is clear that Eric is still in his own stage of grief over his Maker's loss, because the idea of death being a route to peace makes him very angry.
I'm hoping Godric is Hallucination Godric, in much the same way Amber on House was a manifestation of a troubled mind. Plotwise, it would explain why Godric's visit doesn't seem to surprise Eric in the least, given that True Death is supposed to be it for vampires. And it also helps explain why Godric appears in such a saintly vision, when last season, he knew himself to be a flawed being like any other. If he represents to Eric the existential angst that led to Godric valuing a final peace over his relationship with Eric, the anger, rather than love, that surges up in Eric is understandable, as is his desire to remove the possibility of peace for Russell. His anger at Godric's loss is bound up with the loss of his human father and all of those feelings are now aimed at Russell. Eric is more concerned at making sure Russell suffers appropriately than on removing him permanently as a threat, which lets us know he has a good deal of processing left to do for his own grief.
I loved this aspect of the story and therefore, this is one place I really chafed at the limited screen time these characters get. If the writers are going to bring a character like Godric back, then use him in a way that really resonates, rather than seeming a bit like fan service. We need to spend enough time with him and Eric to pick up on nuances such as how much of Eric's anger at Russell is a result of how angry he is at Godric, and whether Eric is actually as grief-stricken and possibly unbalanced as the king is. We get tiny little hints, but all too quickly the show cuts away to one of the other much less interesting stories. This lack of screen time is even more irritating in Bill's part of the plot.