No. 4 Queen - A Night At The Opera (1975)
Another album that owes it's existence to multi-track studios. Like the albums before it on this occasional list, I don't think A Night At The Opera could have existed without the ability to record parts separately, layer them, and mix/edit them into something new.
By this point in time, artists were using the studio as more than just a place to record. studios were now becoming a place to write, work on ideas, and experiment. Often to a degree not thought of in the past.
In the past, studios were a place to record songs that had mostly already been written and played with the structure already in place. Working with a producer and engineers, bands finalized their ideas with a hopefully sympathetic team to realize their potential.
A Night At The Opera changed all that. The band itself had a strong vision, and the chops to pull it off. Expanding the ideas used on their previous album, Sheer Heart Attack, Queen continued to experiment with different styles on the album.
Despite all the ways it could have gone wrong, including songs that prior to that time might be considered too long for airplay, being difficult to recreate live, and generally greatly expanding what a rock band could do; it was a rousing success.
Even tough Freddie Mercury died in 1991 at age 45, this is still an album that gets played and has earned it's place in pop culture. It should also be in your music collection.