"They are starting to look quite threatening really.
"I think we saw [on Sunday] with their defence, that's the sign of a side with character and togetherness and that hasn't been there for some time.
"They are the side that has probably come the furthest and improved the most during this Rugby World Cup and this year. They've got it together, they've got a good culture."
Henry said the win helped Australia on to "the good side of the draw where they won't get smashed about".
"They will get Scotland in the quarter which is the soft game of the quarters with all due respect to Scotland, so they're guaranteed a semifinal place, most likely against Ireland.
"So they are not going to get smashed around next week and are looking good for the semifinals - and who knows beyond that."
Henry felt Argentina had also come on in leaps and bounds in recent years and had been impressed with their Cup performances, pointing out they stretched the All Blacks and had put big scores up against other group rivals.
He also believed Wales were a good chance of beating South Africa in the quarter-finals despite their injury problems and the loss to Australia.
Warren Gatland's men had shown real resilience and their tough group matches to date would help the Welsh compared with the Springboks who had come through a relatively soft pool.
"South Africa are improving," he said. "They are starting to look a wee bit better. I still think they're too old in the tight five. I think they might get found out defensively there.
"I don't see them as real contenders. I think they have probably got too many players who have been there a long time and are probably going down the other side of the hill ... I think the Welsh will give them a huge game."
He encouraged All Blacks supporters to take heart despite some anxiety over the pool matches including Saturday morning's last group encounter against Tonga.
He expected the All Blacks to play a more territory-based game plan now they were into the knockout stages of the tournaments.
"They will be on the job. They will be on the edge of the edge and that's exactly where they need to be.
"I think Steve [Hansen] and company will be pretty happy with where they are at. They haven't hit their straps. They've struggled to get their game together in total so they won't have got ahead of themselves.
"I can remember in 2007, we beat the Italians by 90 in the first game, we beat Portugal by 100, somebody else by about 100 and we played Scotland B.
"So we had no football going into that French game in 2007. The teams we had played against were not good opposition. We gave them all hidings, we looked good and probably got ahead of ourselves.
"There's no way this side will get ahead of themselves, so that's an ideal situation."