Big Star had some strong advocate among reviewers, and they (particularly Chilton) wrote great tuneage, but they were really just one of many. They’re probably best known from the use as the theme to “That 70s Show” — the show creator is no one I’ve met, but we’re very nearly the same age.
I would call them the ultimate cult band. All three of their albums are in Rolling Stones top 500 albums of all time… and nobody has heard of them.