Before the Supremes or Martha and the Vandellas had any success, the Marvelettes were having big hits on a regular basis. The Supremes, who at that time had Florence Ballard as lead singer, didn't chart, while the Vandellas hadn't started then.
With two brilliant lead singers, Gladys Horton (particularly good at the powerhouse songs) and Wanda Young (softer, more seductive), they could do any R+B song with class and style.
After the Vandellas appeared on the scene, and the Supremes made Diana Ross their lead singer, the Marvelettes were markedly less successful despite continuing to make great records, although they did stage a mini-revival on the charts in 1967.
The standout tracks are Please Mr Postman (Motown's first number one hit by anybody, later covered by the Beatles and the Carpenters, who had their biggest British hit with the song), Beechwood 4-5789 (also covered by the Carpenters) and When you're young and in love (one of those 1967 hits, and their only British hit). Britain was slow to catch Motown fever, missing out on their early hits, despite that Beatles cover.
I believe the Marvelettes are the most under-appreciated of all Motown's stars, but their music is as good as any of the others (who I also enjoy). If you like Motown's other stars, you will surely enjoy this collection.