This is some of the best jazz you will ever hear. I still can't believe this was performed in 1961. I don't listen a great deal to 1950s/early 1960s jazz because it seems to me that while there was musical genius at work during that era in terms of creation of many of the great jazz songs and instrumentation, there is generally somewhat of a rough and primitive quality to the music compared to what it has evolved into in more recent decades.
But this music comes across to me as something that might have been created in the 70s or 80s. Gil Evans was way ahead of his time.
To enjoy this music you do need to have some affinity for big band jazz. However, Gil Evans' approach toward big band is very colorful, has lots of dynamic range, and tremendous solo performances, so don't be concerned that it is going to be just a bunch of loud choruses from the brass section.