Before shortening their name as many late sixties bands did (and because of legal action taken from the government Chicago Transit Authority), the band went by and self titled their debut album as Chicago Transit Authority.
Never been a big fan of Chicago, though they are ok for a listen every rare occasion, and I wouldn’t change the radio if they come on. Rock-jazz-orchestra-fusion just isn’t my go-to. I only have some of their albums and this is a solid entry as far as that preface concerns.
There is enough variety (both musically and vocally) here to keep interest across four LP sides if that is your thing, and it is a good place as any to start and see the evolution of this sound.