Multi-national releases are a difficult process. Not only are there linguistic and cultural barriers to overcome, but very often content or simple monetary reasons can keep a game from entering one country or another. Even so, some games are desired despite their limited availability no matter where you are.
That being said, here are the top 10 Xbox 360 games in Japan that were never released in Japan* (Comments are from the owner of the game store, Game Station, which sells imports in Japan).
10: Mortal Kombat Vs DC Universe "The first Mortal Kombat for the next-gen consoles. Highly sought by Mortal Kombat fans and fans of DC heroes like Superman and Spider-Man." (editor's note: Spider-Man is neither a DC property, nor even present in Mortal Kombat VS DC Universe)
9: X-Men Origins: Wolverine "Most games based off of anime or movies are generally lacklustre, however, this title turned out to be surprisingly good. Much like the Toy Story 3 game, which came it at number 11, X-Men Origins: Wolverine is a fairly popular movie-based game."
8: Splatterhouse "An entirely new game in the series. The ability to unlock and play the previous three games is an added bonus."
7: Mortal Kombat "The second next-gen Mortal Kombat. Unlike Mortal Kombat Vs DC Universe, which, much to the chagrin of many hard-core fans, was rated Teen due to the addition of the DC heroes, the new Mortal Kombat was rated Mature, with its staple graphic killing scenes."
6: Aliens Vs Predator "Pretty much all Alien-based games sell well. It's best to play this game after watching all the Alien movies, Predator movies, and Alien Vs Predator movies!" (editor's note: It's really not.)
5: Silent Hill: Homecoming "The Japanese version was cancelled just before release, so this game sells well even now. Recently, people have been buying Homecoming together with the newly released Downpour and the HD collection of the originals."
4: Dead Space 2 "The sequel to Dead Space. It looks like "game sequels never outsell the original." Still, people who enjoyed the original should enjoy this one as well."
3: Prototype "Even people who don't regularly play foreign games often come to our store asking, "Do you have this game called, ‘Prototype?'" Mostly likely it's word of mouth from friends that's making this game popular enough for people to buy it without knowing what it's about."
2: Call of Duty: World At War "This was the only game in the Call of Duty series that didn't get a Japanese release. Whether it's because it was released the year Activision pulled out of Japan, or because the enemies in the game are the Japanese, either way, it's a must-have for fans of the Call of Duty series." (editor's note: My bets are on the latter…)
1: Dead Space "Dead Space is so famous that even people who don't play imported games know about it. The announcement that it wouldn't be sold in Germany or Japan was probably the best sales advertisement ever."
*All data gathered from Game Station and Game Station Online sales from August, 2007 to April, 2012.