I LOVED the miniDisc format.
It was small. Had decent audio quality and had a protective casing. Everything I wanted.
I never felt like Sony pushed the media enough. Being the empire that they were at the time. They could have killed off the CD if they were daring enough.
It has slight comparisons with Blu-ray in some respects. Obviously Sony has had better luck here with market penetration as their PlayStation 3's come with built in. They were very slow with movie industry support like they were with MiniDisc with the music industry.
Who remembers SACD ? Again, failed by their developers (although Phillips were part to blame there) even though its a much superior format to current CD's. Even worse so is Hybrid SACD which has a level of backwards compatibility with conventional CD players.