When you factor in the human element of the players, however, things seem to get a bit messy. Here you have a character who spends most of the time as nothing more than a glorified skill monkey who still travels around with you (mooching gp and xp). In return for him/her doing nothing, this character may go into godmode, making your presence worthless and just reversing the problem.
From the perspective of the godsblade player him/herself, things get even worse. While kicking everybody's rears in a divine fury is awesome, I think that the majority of players out there would find the prospect of doing nothing most of the time to be a bit boring and taxing.
Furthermore, there is the horrifying problem of knowing when to go berserk. If you go berserk in a challenging battle, you often don't have any guarantee that you're facing off against the final or hardest battle to come. Imagine the plausible scenario, for example, of raising your godsblade to assail the BBEG and instantly seeing via know foe that you doomed yourself to a week (or several days, if altered) of inaction to face against a doppelganger or illusion. Any form of misdirection like that simply kills the class (imagine the problems of "going nova" x 1,000).
At the same time, however, using your godsblade as a final resort is equally dangerous for everyone involved. Even though it's likely to eliminate the threat, it will inevitably bring down an additional party member (yourself). If you're the only one still standing when you use your godsblade, there will be nobody left to carry your party to safety when the smoke clears. While your DR would protect yourself fairly well, even a giant ant or kobold would be able to take out everyone else while you snooze.