A friend first recommended this album as I was starting to get into punk. At that point, I was listening primarily to the American strain of punk pouring out of New York.
The Clash are, along with The Sex Pistols and The Ramones, are one of the holy trinity of punk. The Clash are however, musically and lyrically far superior to either of their contemporaries. Whereas The Ramones were still dealing in simple 2 chord power pop, the Clash had begun to incorporate elements of musical styles as diverse as reggae and country. While The Sex Pistols were best known for spouting angry and vaguely general anarchist rants, The Clash were literate and poignant, targetting their political bile at particular social issues ranging from the Spanish Civil War to rampant commercialism.
While the Clash are not as musically sophisticated as their American precursors such as Television, they were among the first to seriously tackle political and social issues while still capturing the youth and energy of the punk movement.