hmm... there is a lot of false information here so i feel obliged to post. but first, i am korean american so i hold those bias. and i dont know a lot of football, but as an asian soccer fan, i feel that the wrong info i post here will at least be a bit more relevant to the post.
historically, asia had three traditional soccer powers. these are S Korea, Saudi Arabia, and Iran. Iran's status as asian soccer power has a lot to do with the individual heroics of Ali Daei who is a legendary player. Saudi Arabia was the first asian nation to get out of the group stages of World Cup. Now some of you might think thats a small feat, but it was and it continues to be a remarkable achievement. South Korea has the longest history of football in asia in terms of World Cup and also in having the oldest professional league in asia.
However since the 1990s Japan has started to perform really well in football. In my opinion, as of 2012, Japan is the best team in asia and is also the team to beat to have the bragging rights for being the best. Japanese are very smart in that they built the proper infrastrure and footballing traditions early on that they are now reaping the benefits of something they planted twenty years ago. These guys are sort of like the "spain" of asia in that they play technical and sophisticated football.
Aside from Japan, Australia has recently joined the Asian Football Confederation. Someone here said that australia joined Asia to go to World Cup easier. this isnt really true in my opinion. before they joined, australia would play some small island nations and routinely pummel them. But this does t help their players improve. Many Aussies are veterans of European football. This is their strength as well as their weakness as they lack domestic soccer developement. They dont have the numbers so sometimes its hard for them to get a complete team of very good players. Despite this, they are easily within top three in asia.
Going back to Saudi Arabia, these guys are recently having some problems. I dont follow the Saudi league so you will have to ask a Saudi about what is going on over there. Generally speaking however, the Saudi sheiks have a tendency to screw up their soccer developement. They never ever sell Saudi superstars to europe, so their top talents are held back from developing further. They change their top managers at the slightest whim of failure, so their team is in a constant state of flux. And some Saudi fans say some players are over payed and their incentive to play well have been destroyed. Despite this, one cant underestimate Saudi football in asia, as when they do come together they play quick counter attacking creative football.
Now Iran is like Saudi in that they too play quick counter attacking creative football. In asia, the Saudi Iranian rivalry is famous, and their matches are delightful to watch as they would see saw. Iranian problem is also a lot like Saudi in that the Shia clerics interfere in Iranian football. Ofthen their footballing body does not adequately support their team. However, the top players of Iran plays in Europe and they bring these talents with them when they play in asia. in my opinion, they are currently number four of Asia.
I would place the Uzbeks as number five of asia. these guys have inherited Soviet football. Their players are physically strong and many asian countries have a hard time dealing with that aspect of the game. Howevee, sometimes they just dont play well, which is why they are at number five. Many of their players play in Russia, and are genuine stars.
Besides these countries you have from west asia countries like UAE, Kuwait, and Qatar who can still give a good scare to the above five countries. But they tend to be small countries and the talents of their top super stars get diluted by their not so super teammates. Qatar is an interesting case as they have a tendency to nationalize brazillians to get some oomph into their team.
Iraq used to be an up and coming Asian soccer power and they used to give South Koreans some heat. But Saddam Hussein decided to destroy the footballing culture of both Iraq and Iran. But whereas Iran recovered, Saddam's son Uday would mess around with Iraqi football and they didnt reemerge until Uday was killed. We all saw this in the form of the 2007 Asian Cup where they played really beautifully, except some not so flattering grass rolling. However that is still "fair" game. I have no idea where Iraq is in the world of football now.
In east asia, there is still China and North Korea. North Korea is an interesting case since these guys only appear rarely, and when they do, they give a good scare to everyone. North Korea is infamous for defeating Italy in the 1966 world cup with their "cheollima" football. They also gave the Portuguese a good scare in the same tournament, scoring three goals in the beginning of the game. It was the brilliance of the soccer legend Eusebio who saved Portugal from total defeat and ended the game 5-3 portuguese victory. North Koreans have a few stars playing in Japan, swiss, russia, and even in south korea. it is a testament to their love of soccer that their government would allow these guys to play outside. However, many of their domestic players have never been exposed to world football. They still should be regarded within top ten in asia.
Now there were a lot of Chinese posters here who despise S Korean soccer. A lot of this has to do with the fact that the Chinese team do particularly poorly against south korea. They dont have this when they play against the arabs or japanese, but their media is absolutely unforgiving when they lose to Korea. This is a large factor in why China sometimes make top ten and sometimes it doesnt. China like all these other countries also have super stars. Many play in England and some of them even played in South Korea. China sometimes sabotage itself when they allow their emotions to over take them while playing the game. And their fans are absolutely brutal and dont support their own team. But on the bright side, the country is an avid footballing nation and they still have the future on their side. This team borders on top ten flipping on the upside or downside depending on temperament.
Besides these nations we also have countries like Vietnam and Thailand who love football, but have inadequate footballing infrastrure.
As for India, there was a time when India was more interested in football. unfortunately they stopped caring somewhere down the road, but FIFA and AFC are always scheming to have India, a countey of a billion people back into the fold. only the future will tell where India will be.
you might want to visit bigsoccer dot com if you want more asian footballing analysis, as i said before, i know very little about asian football and most of what i wrote is gibberish.