While I agree with Soldarnal's analysis, this question is interesting enough that I would like to play devil's advocate. I've been mulling over the issue all week so bear with my (overly-long) answer.
The setup of Job is the Adversary looking for a way to discredit God:
The Adversary answered the Lord, “Does Job not have good reason to fear God? Why, it is You who have fenced him round, him and his household and all that he has. You have blessed his efforts so that his possessions spread out in the land. But lay Your hand upon all that he has and he will surely blaspheme You to Your face.” —Job 1:9-11 (NJPS)
On the surface, the charge is that Job only fears Gob because he receives material blessings (and in chapter 2, because he is protected from physical suffering). But close under the surface stands the charge that God bribes His people so that they will love Him.
The text tells us explicitly what Job might have done to cause the charge against God to be found true:
Then Job arose, tore his robe, cut off his hair, and threw himself on the ground and worshiped. He said, “Naked came I out of my mother’s womb, and naked shall I return there; the Lord has given, and the Lord has taken away; blessed be the name of the Lord.”
For all that, Job did not sin nor did he cast reproach on God. —1:20-22 (NJPS)
His wife said to him, “You still keep your integrity! Blaspheme God and die!” But he said to her, “You talk as any shameless woman might talk! Should we accept only good from God and not accept evil?” For all that, Job said nothing sinful. —2:9-10 (NJPS)
Job's wife's suggestion is that he throw in the towel on a relationship with God and give up on life. But Job easily rises to the challenge and does not sin.
At it's center, Job is a poetic dialogue with his three friends. Job pleads for God to answer why he must endure suffering and pain. He appeals to God for vindication since he is a righteous man. The replies from his friends are accusations that punishment came because of Job's sin, which the reader knows is the precise opposite of the truth.
So Job is stuck between a rock and a hard place: he's not going to cast reproach on God for taking away what he was given. But he can't accept the charge that his suffering was the result of sin either. Remember that in the first two chapters, God explicitly affirms that Job is "a blameless and upright man who fears God and shuns evil." Accepting the charge would serve God's Adversary just as well as direct blasphemy. It would make God to be a liar.
The Trial of God
Along the way, Job's friends act as Job's accuser and since God has picked Job to be His champion, they are acting as God's accusers too. Now there's no indication that either Job or his friends are aware of the heavenly drama told in the prologue. But just as the Accuser puts God to the test in heaven, Job's friends put him on trial on earth. And Job acknowledges that he would like to put God on trial as well:
Indeed I know that it is so:
Man cannot win a suit against God.
If he insisted on a trial with Him,
He would not answer one charge in a thousand. —9:2-3 (NJPS)
And in his final speech, Job swears that he is innocent:
By God who has deprived me of justice!
By Shaddai who has embittered my life!
As long as there is life in me,
And God’s breath is in my nostrils,
My lips will speak no wrong,
Nor my tongue utter deceit.
Far be it from me to say you are right;
Until I die I will maintain my integrity. —27:2-5 (NJPS)
Elihu the clever
I disagree with the common belief that Elihu was essentially correct in his theodicy. Rather, Elihu cleverly reiterates the accusations of the three friends and supplements them with the assertion that God will not answer Job's case against him. In many ways, his arguments ring true: God does punish the wicked, uses suffering to discipline the righteous, and, even when He answers Job, God does not justify Himself. (God doesn't even explain what was going on in heaven!)
But Elihu's arguments come directly out of the Adversary's playbook:
Who placed the earth in His charge?
Who ordered the entire world?
If He but intends it,
He can call back His spirit and breath;
All flesh would at once expire,
And mankind return to dust. —34:13-15 (NJPS)
Elihu's argument might be summarized as:
- God's job is to create us and give us good things.
- If we disobey Him, He will use pain and suffering to punish and correct us.
- We can't expect Him to respond to our complaints since He is always just and we are never right to complain.
If you remember from the first two chapters, the Adversary hopes to discredit God by removing God's blessings from Job. He hopes to prove that the way God wins love for himself is by rewarding those He favors with good things and correcting those who stray with pain. Elihu's words are theologically correct, but they don't address the greater truth that God wants a relationship with people. If Job accepted the simple explanation that God is punishing Job for some unknown sin he'd committed, Job would be giving up on his relationship with God and thus winning the bet for the Adversary.
God has the final word
Finally, God speaks. I argued elsewhere that God finds Elihu beneath contempt, but here I note that while God does pass judgment on Job and his three friends, He does not explicitly deal with either the Adversary or Elihu at this time. Surprisingly, His speech does not seem to answer Job's charges either. He first asserts His dominion over the physical (Job 38) and animal worlds (Job 39). Then He prompts Job to make a short reply and proceeds to proclaim authority over the behemoth (Job 40) and then Leviathan (Job 40:25-41:26 in the Tanakh and Job 41 in most English translations).
Seemingly, the behemoth (a superlative beast) and Leviathan are part of the animal world that God already showed authority over in chapter 39. But a reasonable reading might be that these are mythical creatures that represent evil. Unlike their representation in Babylonian mythology, however, God made the behemoth:
He is the first of God’s works;
Only his Maker can draw the sword against him.—Job 40:19 (NJPS)
Unlike humanity (which does have dominion over animals), God has dominion and authority over the Leviathan and is able to capture him and bring him into submission. Job accepts these words as a proper answer to Job's charges against God, which only works if God metaphorically had declared His dominion over evil itself. Job 42:1-6 signals his acceptance of God's promise to tame evil. The conclusion of the book shows Job's trust to be well-founded as he finds justice for himself and his three friends.
God's justice against the Accuser is delayed
But we don't see God enact justice against the Adversary or against Elihu. I do not believe this is an oversight by the author. Rather, it seems we are, like Job, to trust that God will set all wrongs right in the end. The final end of the Leviathan is addressed in other Biblical texts such as:
In that day the Lord will punish,
With His great, cruel, mighty sword
Leviathan the Elusive Serpent—
Leviathan the Twisting Serpent;
He will slay the Dragon of the sea. —Isaiah 27:1 (NJPS)
If the author of Job truly equates the behemoth and Leviathan with the Adversary, it would seem that is also his fate. And if Elihu truly opposes God, it's not a stretch to identify him with the Adversary of chapters 1 and 2.
Good lies often include true statements
What makes Job a tough nut to crack is that Job's friends really don't stray far from the truth. Even Elihu presents ideas that are largely previews of what God will say in conclusion. There aren't a lot of verses I can find that seem to be theologically wrong (either to the Jewish understanding or my own Christian understanding). If the serpent in Genesis 3 and Satan in Matthew 4 are the same person as the Accuser of Job, we shouldn't be surprised to hear true, but not complete statements from his imitators. God is angry with Job's friends because they said things that are not true about God, but I'm hard pressed to identify anything they said that was wrong.
Worse, I see God repeating many of the same arguments that we'd already heard from Job's friends. The two things that God adds to the conversation (it seems to me) are His own voice and the description of the end of all evil (chapters 40 and 41). Job asks for God to answer him, his friends don't offer any hope that will happen, and yet God does come and reveal that all will be set right in the end.
Finally, I see Eliphaz, Bildad, and Zophar in much the same light as we see Peter in Mark 8:31-33 (HCSB):
Then He began to teach them that the Son of Man must suffer many things and be rejected by the elders, the chief priests, and the scribes, be killed, and rise after three days. He was openly talking about this. So Peter took Him aside and began to rebuke Him.
But turning around and looking at His disciples, He rebuked Peter and said, “Get behind Me, Satan, because you’re not thinking about God’s concerns, but man’s!”
They aren't identical with Satan, but they are speaking his lines. Remarkably, Peter argues in a very similar vein to Job's friends: God doesn't require innocent men to suffer.