Diadem of Maunstraut is the first full-length King's Field fangame made with Sword of Moonlight (1) to be in the English language. The game has a concept similar to the traditional King's Field games (and other games of the series) as well as its own original soundtrack.
There is one major known issue with the Sword of Moonlight engine. (Special thanks for John for finding this out.) Sword of Moonlight has a recognized memory leak. Essentially, it loads data into the RAM but then it doesn't unload it. When the collected memory usage reaches a certain point, there can be major slowdown and unresponsive gameplay. (In my opinion, this might be why the Sword of Moonlight software never reached the US)
A large deciding factor of the severity of this issue depends on the computer's schematics. My computer starts to get slowdown on traveling to certain new maps (Maps are divided by in-game greetings and different music) and sometimes, depending on the areas, there can be severe frame-rate issues. My dad's computer doesn't get slowdown on all newly visited maps, but will show minor skips if multiple areas are visited in succession. (4)
Since there is no source code for the EXE file, remedying the memory leak itself is not an option. However, there is a solution: Saving the game, closing Diadem of Maunstraut, restarting and loading whenever the first signs of slowdown occur directly addresses and arrests the problem. Doing this completely frees all RAM that the program has used and restores gameplay to a smoother state. Depending on the computer and the rate of exploration determines how often a game restart is recommended.
Since new maps seem to be the main trigger to the game slowing down, extra save points are added at the end and beginning at each place maps are switched. If the new map is experiencing slowdown soon after entering, simply examine the save point there, restart and reload your Diadem of Maunstraut game.
Tom Eversole - Map design & item/object/enemy placement and schematics, soundtrack and artwork
John Osborne - Sword of Moonlight translations, patches and fixes, additional Diadem of Maunstraut objects and items
(1) Sword of Moonlight: The King's Field Making Tool is a computer program to build King's Field games.
http://www.fromsoftware.jp/main/soft/som.html
(2) JDO Translations specializes in converting Japanese language software and games to English
http://jdo-translations.100webspace.net/JDO.html
(3) Mark (Duhrin) goes into detail throughout a YUKU post, the death of King's Field
http://agetec.yuku.com/topic/1758
(4) Memory leak tests are determined on a continuous play base.