Yeah, your situation as an ALT is designed to be good. You rent an apartment from the school/BoE and have a different contract from everyone else and generally don't have to deal with the things regular Japanese people have to do.
Generally, there are a lot of great things about Japan... Onsens are great, and transportation outside of roads tends to be excellent but expensive. Roads, however, cost a lot of money to utilize and are often narrow (freeways here are 2 lanes, 80km/h speed limit), in disrepair, or redonkulous. (My city has bridges for cars that look like they were designed for bicycles.) It's easy to travel within the country, because everything is very compact, and there's a lot of beauty, as well as urban sprawl to explore. Food is incredible, I think. I love sushi, udon, soba and all that-- though, to be honest, I hate anything involving "courses" here, which are popular at enkais. Another nice thing is that you can get mostly everything you can get in the States here SOMEHOW, whether it be ordering from overseas and having it shipped to you, or finding the one random online shop that stocks it here in Japan. Ah, that's another great thing-- shipping here is typically a one or two day affair at most, anywhere on the main island. COD is, while somewhat expensive, a great, great thing.
As an ALT, my hours are great. I work from 8:00 to 4:00. I don't have club activities, I take a lunch everyday (instead of eating at school, like most ALTs), and I don't go to long staff or teachers meetings. My rent is cheap (I pay about $200 USD every month) for an apartment that is 10 minutes from the main station in the middle of town. I have fiber optic internet, money to spend on travel and my hobbies, and lots of time to do whatever I feel like.
However, even within our city, ALT situations vary quite a bit. We have 3 ALTs living out in the middle of nowhere, all three about 20 minutes from the station by car (or more) in two directions. They pay similar rent, the smaller apartments a little less, the larger house, a little more. Due to the way our city is laid out, we all have cars, so we all pay shaken and road tax every year. I can drive 5 minutes to McDonalds in the middle of the night if I get hungry, but our other guys might have to drive 35 minutes to eat that same meal.
The disadvantages to living here are, superficially, few. (As an ALT) Assuming you have a good job and maintain a healthy lifestyle you'll probably never be bothered for anything. As safe as this country is, I know a few people personally who have been victims of theft and crime, so it's not all roses and flowers on that front. (And, despite having lived in one of the most crime-ridden cities in the USA (Washington D.C.) and on the border of Juarez, Mexico, I've never personally been a victim in any crime, here or in the States.) Driving here can also be dangerous. I've never been involved in an accident but my best friend here was T-boned by a 20-something girl and had to face insurance penalties (even though it wasn't his fault-- in Japan, both parties are always at fault; in this case, responsibility was "90%/10%") and buy a new used car to replace the heap of scrap she left in her wake.
However, as an immigrant, you face a different set of challenges, I think. You won't have that ALT contract to fall back on, and you may be required to work the ridiculous hours your Japanese colleagues work, and go to all their functions, and participate in society the same way they do. You may be asked to move away from your family for months or years at a time for your job, without any recourse short of quitting. I used to have an English teacher here who would tell me he drank every day alone in his house and "sometimes" saw his wife and kids on the weekends if he wasn't too tired to drive 3 hours up to see them. Another teacher of mine would often take an expensive train in the evening after work to be with her mom (who was having some sort of trouble in a completely different prefecture) for a few hours before hopping on an early morning train to get back to work on time the next day. Another one spent an hour and a half commuting every morning to work (work starts at 8AM) and another hour and a half commuting home at night for 3 years before she was finally moved to a school within a reasonable distance of her home.
I find the things that bother me the most now involve the odd attitudes and misunderstandings that people have. Frequently, when I show people pictures of something back home, or tell stories, Japanese people are amazed: "You have fireflies in America? I thought that was Japanese..." "What, you fly kites in America? Oh man, I never imagined people in other countries did that," etc. etc. It was very difficult too, getting used to the idea that the customer isn't always right, and no, the salesperson can't open that package up to show you the product itself, and no, you won't be able to find insurance for your electronics because no one does that here in Japan, sorry. Sure, there are plenty of stores that allow you to play with their products (large electronic stores in big cities, music stores, etc.) but if your request doesn't fall within the normal range of requests, there's very little chance you're going to find someone who is willing to risk their job or lift a finger to help you. And finally, Japanese people are fiercely dedicated to the way they've always done things, and even if there's a better way of doing it they'll likely stick to the tired and true. I see students sweeping the dirt off the concrete OUTSIDE every day as though it makes a difference and I change my shoes every time the floor changes textures even though there's no real, honest reason to do that.
Furthermore, goods are expensive here. I'm not sure about Europe, but compared to the States, most everything has a premium here. I buy canon lenses, and right now prices here in Japan are $100-500 (for lenses falling within the $400-1500 range) more than the USA prices. Televisions too are incredibly overpriced. Shopping at Amazon.co.jp allows you to get away with prices that are only a few hundred over similar American televisions, but go to an electronics store and you're looking at hundreds or thousands more than you should be paying for a similar size/resolution TV in the states. I think the best prices I've seen for TVs here has been at Costco, which as expected, was doing gangbusters business.
One of the largest challenges of living here is just getting used to not having the same opportunities you would have in your native country. Your job is going to be determined by your ethnicity and/or level of Japanese and there's not going to be much chance to move up the corporate ladder or anything like that. Depending on your level of Japanese, you may find yourself ordering a lot of books and downloading a lot of television to pass the time. Your friends and relatives will be back in your home country, telling you they want to see you and you'll be thinking about the cost of a plane ticket and how hard it is to sit in a plane for 9 hours. And finally, if you're working as an ALT, you'll find that even if you have great kids and great schools, your job is still mindless and not at all fulfilling.
Edited: 2009-05-20, 11:16 pm