I'm an Aussie who is fortunate enough to have been to every Disney Theme Park (at least until Shanghai opens) and Tokyo
Disneyland remains my favourite. Possibly because it was my "first" Disney Theme Park and also because it is located in my favourite foreign country.
The main reasons I enjoy Tokyo Disneyland in comparison to the other theme parks is the crowds (and resulting atmosphere) and the food. I travel with my partner and sometimes as a childless couple, we feel a little out of place in a lot of the other theme parks. This can be especially evident when we're waiting in line or dining and it seems that we're surrounded by families and their often screaming children (and parents).
But, Tokyo Disneyland appears to attract a lot of adult couples and extended families with people from all generations (babies through to grandparents), so we don't feel like the odd ones out (even though we're clearly not Japanese). Also, all the locals who travel to Tokyo Disneyland seem to do so with the attitude of having a great time whereas in the other parks, we get the distinct impression that many families are only there because it's something they have to do for their children and it can be very clear that not everyone is enjoying themselves. In Tokyo Disneyland, no matter their age, everyone seems to be having a great time.
And out of all the parks, I found the food to be consistently good in Tokyo Disneyland. With a lot of the other parks, I've found the food to be hit or miss, irrespective of the price point. But, in Tokyo Disneyland, the food has always been awesome.
And I love going to Tokyo Disneyland because it means that we also get to see parts of Japan (and South Korea) and I love travelling throughout Japan. In contrast to some of the other comments, we usually book flights when they're on special (for as low as $400 return) and we find that prices in Japan are usually cheaper than in Australia (although we do travel on a pretty tight budget).
I wouldn't travel to Hong Kong Disneyland as often because there isn't quite as much to see and do in Hong Kong, without also journeying to mainland China (at least until Shanghai Disneyland opens). And while I enjoyed the park, it just didn't have the same appeal as Tokyo Disneyland.
I also enjoyed the US parks, but due to the flight times and costs, I feel as though I need to take at least four weeks leave to travel to the US whereas I think two weeks is sufficient to travel to Japan. I feel the same about Paris Disneyland, as I'd really only visit there as part of a much longer, European holiday.