Whether you'll like this film or not will probably depend on what you consider an "important" film and how much weight you put on that. Technically it's all very barren and limited, but Burnett's uncompromising look into one of the poorer (and black) neighborhoods of LA certainly has worth.
There's no real story to speak of. We follow a family (the father works in a slaughterhouse for sheep, hence the title) and see them in their natural habitat. It's a series of small vignettes that paint a picture rather than tell a story, which is fine for this type of film. Just don't expect to be entertained by a narrative.
The camera work is pretty limited, performances are weak and the barren style certainly isn't my preference. But the choice of music is pretty decent and several more poetic moments give Killer of Sheep a bit of extra flair. Not a film I'd ever revisit or recommend, but if you like neo-realist cinema and you wouldn't mind a 70s USA flavored version, it can't hurt to give this one a try.