The Mini-Disc was a great technology. Too bad it didn't catch on. Unlike CD's its' almost impossible to scratch a mini-disc. MD's were recordable, and re-recordable, from the get get go. MD's are the perfect size. Initially MD's had a proprietary compression scheme ATRAC that was much better than MP3, in terms of sound quality. With the advent of blue lasers MD's were able to use full uncompressed data and get more than a CD's worth of music on them.
Sadly, it's one of those really geat technologies that just died off. I don't know if you can even buy an MD player/recorder today, and certainly no pre-recorded media is available in that format.
RIP Ohga-san.