Fwhaap! "Awe, my nads. Stupid Seoul Metro system." As an American, especially one coming from a city with no internal rail system, I'm really not qualified to be talking about other countries transit systems. As a world traveler who's been to almost every country in Asia, I feel entirely justified in doing so. I just got back from returning my Delhi Smart Metro cards. Trains are by far my preferred method of public transportation, but some countries have better systems than others. I've spent a lot of time riding and analyzing different metro systems around Asia, and the following are things which separate the good from the bad:

Signage:

As a traveler, signage is one of the most important things. Locals don't often need the signs because they know where they are. Good metro systems have full system maps at many places throughout the station, including the ticket machine/window, on the platform and in the cars. Good systems also have consistent maps. The maps at the station are the same as the maps in the car and the same as the paper maps at the tourist information center. Good systems also have signs using Latin characters.
The best: Hong Kong
The worst: Japan

Convenience:

Convenience really breaks down into a couple components: availability of long-term passes, frequency of trains, locations of stations and security hassles. Some cities offer rechargeable metro passes which save you the trouble of getting single journey tickets. South Korea is the best in this regard as you can get one pass which works for the metro system (including buses) in most of their major cities. Taipei deserves an honorable mention as they have a special tourist metro pass. As far as frequency goes, Beijing takes the cake; there's always another train within two minutes. In Hong Kong you're never very far from a metro station. Some cities require you to go through a security checkpoint of varying scrutiny before entering the metro system. In Beijing you'll be forced to drink some of any liquid you're carrying. In Manila you get to stand in line for one hour before a full cavity search. Never, in 5 months of traveling, had a security officer actually wanted to go through my entire pack until I got to Manila.
The best: Seoul
The worst: Manila

Cleanliness and bathrooms

It's simple: no one likes a dirty subway system and when you gotta go, you gotta go. South Korea excels in both these aspects and the metro bathroom is often the preferred and reliable public bathroom. Japan obviously keeps things clean, but to be honest, not really any cleaner than almost every other country, with the exception of Malaysia and The Philippines.
The best: South Korea
The worst: The Philippines

Not making you look like an idiot:

No one wants to look like an idiot, especially in a foreign country. You already look like enough of an idiot standing their with your giant backpack on, so it's nice when a metro system does nothing to add to that feeling. Imagine you're standing on a train. You know your stop is coming up soon but you don't know exactly when or on which side the door will open. Being anxious, you go and stand in front of the door. The train stops: it's your stop and you're facing the wrong door. You push and fight through the crowd to get to the opposite side of the train and just barely escape as hoards of people are rushing on. Wouldn't it be nice if the car had a full system map showing you where you currently are, where the last stop was and what stop you're coming into, as well as having an indicator telling you which door will be opening? Hong Kong has all that. Now imagine you're walking up to the entrance machine and you swipe your ticket: nothing happens. You swipe it again and it opens. No big harm. Imagine that instead of having the barrier closed and opening it when you swipe your ticket, the barrier starts open and closes if there's something wrong with your ticket. You swipe your ticket, receive no indication and start walking through the gate. Then a piece of plastic swings forward and hits you in the nuts. You stop short and there's a pileup behind you. Now you have to push back and re-swipe your ticket and hope things work better next time. This is the way things are in South Korea and Japan.
The best: Hong Kong
The worst: South Korea

How to stand on the metro:

Speaking of looking like an idiot, there's few better ways to look like you've never ridden a subway before than to stumble around every time there's a kink in the track. I was fortunate enough to learn to ride the metro in Singapore, a country of people seemingly bread to stand on trains. As I was holding onto the hand rail and still bouncing around, I noticed that the locals didn't appear to move at all. I saw one woman with stilettos on scratching one leg with the other, not holding onto anything, not even seem to notice a bi-directional jolt to the train which almost put me on the floor. At first I tried to anticipate the movement of the train and lean away from the direction I was about be jerked. That approach didn't work so I started studying the locals. Their heads appeared to stay in the same place. They didn't move their feet. They weren't leaning. "How are they doing this?" I wondered. Then I remembered the words of Chubs Peterson: "It's all in the hips." Over the next year I slowly developed my technique. If you succeed in following these steps you'll look like a local (apart from the giant pack on your back and probably your skin color):

1. Stand with feet shoulder width apart, at roughly a 20 degree angle off the direction the train is moving. That means you should mostly be looking to the side of the train, but not perfectly aligned with the car. Most of the train jerks will be in the direction of motion, but it's the side-to-side bumps that are most likely to throw you. This stance should account for both.
2. Try to keep your head and feet in the same place. Before leaving a stop, swing your hips toward the front of the train. Before coming into a stop, swing your hips toward the back of the train.
3. Try to counteract all motion only by moving your hips. Remember, keep your feet and head where they are.

Conclusion:

There's a lot of things that go into making a good metro system and there's quite a bit of difference between the Asian countries. China was surprisingly good and far preferable to Japan in every regard. South Korea has the biggest split, with lots of things done well and lots of things done very poorly. Google Maps indexes all the metro systems and gives accurate directions wherever you are, but if you're in Japan or South Korea they'll only be in Japanese/Korean characters respectively. I view this as an issue with Google rather than either of those countries, but as a testament to modern technology, when Google says a bus or train will be somewhere in Asia at a certain time, you can pretty reliable count on it being there. I love trains: they're easy to navigate and far more reliable than buses. In many ways Asia is trying to catch up with the America, but this is one place where America is embarrassingly behind.