Australian and New Zealan wines are some of best in the world, even according to a lot of the French experts. The French would never admit this unless it was a very well established fact due to their national pride with regards to their own wines.
American wines are generally regarded as pretty poor with the US wineries catering for popularist trends in the wine market as opposed to developing and nurturing high quality grape varieities over generations. Many US wineries simply cultivate a robust root stock to which they graft the new trendy grape variety for the next season onto and then cut the vine off after harvesting.
The Australian and New Zealand wines are mostly made in the French tradition with regards to grape varieties and process of wine manufacture.
However, even today there is still a core of wine experts who claim that nothing can beat the old world wines of France, usually you will find they have a vested interest in those wines in terms of their business interests.
Alexpeddle: you really many an interesting case against Australian wines. I think you are are wrong but that's okay, everyone is entitled to an opinion.
One thing neither of us remembered to tell the asker is that a good wine is one they find they like, irrespective of price, nationality, region, style or age.
After having toured aussie wineries (can't say anything about New Zealand, haven't had them), I have to say their wines are some of the worst I've had. The wineries were unpleasant, and their wines were so acidic and unbalanced to flavor that they were quite unpalatable. It's no wonder they can ship that crap to America and sell it for roughly $6 a bottle. They sell it cheaper here than you can buy it in Australia, after shipping it half way around the world. It's no wonder that the best wine tasting I had in Australia was at a local fair, that was selling premium European wines. Hard to beat a real German Riesling or Gewurstraminar when you've had that crap they pass of as a Riesling in Australia. It's hard to turn down an Italian Syrah, when you've just drank some bitter paint thinner called an aussie Shiraz. Had an Italian Cab Sav there that knocked my socks off, which was much better than the aussie cab savs that just made the skin dissolve off of my tongue. I'm sure there is good wine made in Australia, but from my large sampling, they were far and few between. I'm used to going to wineries where I have a hard time deciding what not to buy, because all the wines are so good. In australia, it was difficult just finding a winery that had a wine worth buying.
Edit:
I must reply to Mustang in saying that France would not have wines if not for the American hearty root stock. And the old world French style wines are highly overrated, and sell more by old world reputation, and not by new world quality. They have become complacent by thinking their grapes are far superior and can not keep up with the modern techniques and varietels. As for Australia making their wines to strict French control, that would make sense, if Australia's climate, soil, and growing regions were similar to that of France, but they are not. However, the grapes make really unbalanced wines, and most of the wineries don't do anything to combat this. It is made even worse by using pure varietel wines, instead of blending their wines to add some balance. I must say, the one place that I did like all of the wines in Australia was at a monastary. Their wines were made of grapes that grew well in that area, and they knew how to blend the wines for perfect balance. I guess God new something more about wine making than the French did.
Final Edit: I just want to point out, that people from Australia think they have great wines, because thats all they can really get there, the liquor stores don't sell any other type for the most part. When Aussie wines are all you can get, then yeah, they probably taste pretty good. But remember, they also eat Vegemite there and think it is really good. Any sane person can agree that vegemite is not a tasty treet.