The Raiden Series is still one of best arcade shooters to date. All the Raiden from Raiden II, DX, Fighters, Fighters II and Jets are absolutely great in graphics. To answer your question Why it's not emulated. The sprites are encrypted, and apparently very well. The various people who've cracked the Neo Geo, CPS 1 & II,PGM, Sega 8-bit, and other encryptions have all run screaming from it. Only game that you will see it on any console is the playstation the Raiden project and Raiden DX on PS japan import. I hope in the future someone can emulate Saibu Kaihatsu SPI System: