A few thoughts: It's pretty uncommon for the twist ending of a movie to become far more popular than the movie itself, but I would argue 'Soylent Green' is the first instance of just that. This is a murder mystery set in a dystopian version of the future where the greenhouse effect has ravaged the food supply, and the government has engineered a new superfood to combat the wide-spread starvation called - wait for it - soylent green. Sadly, almost 45 years after the film's release, you'll be hard-pressed to find anyone who has heard of this movie who hasn't also been made aware of the final twist. I won't spoil it for anyone who might be reading this, just know that your experience will be made far more fulfilling if you go into this not knowing how it ends. It's not a bad movie, the acting is solid and the setting is appropriately dark, but the ending really is the main reason to give this one a look. It's not an ingeniusly crafted mystery, but it is an iconic resolution and shouldn't be dismissed as anything less than important in its own way.
Who would I recommend it to? Anyone who wants to see the source of one of sci/fi's most famous twist endings. Fans of mysteries might be entertained.