I had the original vinyl Sgt. Pepper in mono when it first came out. It was so much cheaper and I didn't have a stereo player at college so I bought it. Then when I got a stereo player, I bought the stereo Sgt. Pepper. Stereo was much better sound, and the psychedelic sound effects were amazing. Nowadays everyone thinks of the sound of Sgt. Pepper as being taken too far, but the idea was to try and mimic the aural distortions of tripping, and other drug use. I can't really judge how well they succeeded in that, but when played over speakers, the album was so different and interesting that there was no doubt in my mind that the soundtrack in stereo belonged with other works of abstract art. They were not trying to reproduce the sound of the concert hall or any other live recording venue. Instead, they made a recording that creates its own space where the ordinary senses become by turns enhanced and obscured and distorted. This could only be fully appreciated with speakers, listening to the album in sequence as put out, one track blending into the next.
On headphones, it's just too confusing and disconcerting -- imo, something that seems like a schizophrenic experience of sound delusions and hallucinations. There are many who love it. I can't. On speakers, however, it's as if the music were refracted through an amazing diamond like prism into its component tracks of vocals and instrumentation, each of which move in, out, and around the soundstage.