Koshien Stadium in Japan, 2007; courtesy Wikipedia via the GNU Free Documentation License
Via MLBTR, I ran across this interesting article comparing all the parks in Japan, both to each other and to stadiums in MLB.
In general, the article says that Central League stadiums (the league in which Kosuke Fukudome played, although there are now interleague games in Japan as there are here) are smaller than Pacific League parks. However, Fukudome's home park, the Nagoya Dome, is relatively new (1997) and its dimensions are among the largest of the Japanese stadiums. Finally, Japanese stadiums, especially the newer ones, have (in general) taller outfield walls than US baseball stadiums.
There's a graphic with all the dimensions in this article, and a photo of Hanshin Koshien Stadium, the oldest and most revered of the Japanese parks (see this site for more; it's got ivy growing on the outside. Seems sort of like the Wrigley Field of Japan), taken during the annual Japanese high school baseball tournament (which the writer, a Canadian who lives in Japan and works as a translator, calls "culturally similar to March Madness"). I personally have been to both the Tokyo Dome and Seibu Dome. The former is similar to the Metrodome and Tropicana Field; the latter an outdoor park that was retrofitted with a roof (which doesn't completely enclose it, just keeps most of the wind and rain out). Both of them have dimensions not dissimilar to most modern major league ballparks.
Since we now have a regular poster here who actually lives in Japan -- maybe dragonsfanatic can take a look at this site and let us know his take on it, especially as it relates to how Fukudome might do in his first MLB season.