Australia's most capped player said the standard of rugby from the Home Nations, particularly the Celts, has been a huge disappointment.
A win over Italy put Wales into the quarterfinals, but Campese fears for the Welsh even before they get there, with a final pool match against New Zealand on Sunday.
Scotland were thrashed by France last week and must beat the enterprising Fiji to reach the last eight, Ireland is there but struggled past Argentina and England was given the shock of its life by Samoa.
"God knows what New Zealand will do to the Welsh," Campese wrote in his column in English newspaper The Times.
"I remember the great Wales teams of the 1970s, they were truly inspirational. The game in Wales seems to be falling apart.
"But it's not as bad as Scotland. I don't think I have seen a bigger rabble. They will be really lucky to beat Fiji on Saturday and, on the evidence I've seen, they don't deserve to. I don't know why they are here. They haven't got a clue, no game plan and no players."
Campese questioned how Ireland, runners up to England in last season's Six Nations, escaped with a 16-15 win against Argentina on Sunday.
"Ireland just froze and were awful, dreadful. This is the second best team in the Six Nations Championship. Come on,!!" he wrote.
"I can't see them having a prayer against Australia. That means they will face France in the quarter-finals and there will be only one result there."
The great winger then went on to his favourite subject - criticising England.
He first had a go at the world's No.1 ranked team for fielding 16 players for 34 seconds late in its 35-22 win over Samoa on Sunday and then questioned out-half Jonny Wilkinson's ability under pressure.
"Did they go to school? How can you have 16 players on the field for 34 seconds and not notice?" he wrote.
"Clive Woodward's boys were caught napping and found it tough against a side that is unpredictable and doesn't play to a structure.
"Jonny Wilkinson is finding life tough. He's under so much pressure to perform ... he looks ill."
Campese said it was too late for England, as well as South Africa and Australia, to change the game they play.
Wilkinson himself said he had never played in a game like the one Samoa forced upon England in Melbourne on Sunday.
"I have never experienced a game like that, that has started like that, where a side has torn into us with a ferocity like that, come on to the ball like that, piled on the pressure and then scored a try like that," Wilkinson wrote in his column The Times.
"It was so intense. That stifling atmosphere, that enclosed stadium, loud, fast, frantic and so much going on. It was a case of trying to keep your head."
Wilkinson also touched on his missed penalty goal attempt from in front of the posts. "This might sound surprising, but I'm honestly happy being able to say, so what?"