I've always thought of it as really campy, but the ending of Soylent Green sort of made me smile when I was a kid. I learned later that the novel didn't even have cannibalisim in it, yet as a kid, I don't know, there was just something about it that made it good. Though the whole movie was for better or worse good.
On the off chance that I would find that again I tried to find some movies that were similar. My search efforts returned these results:
- Local Hero (1983)
- Miracle Mile (1988)
- Millennium (1989)
- Dark City (1998)
- Knowing (2009)
- Take Shelter (2011)
You could watch the trailers on YouTube, but for the older picks you would be wise in knowing that old trailers are crap. They pretty much just show the whole movie in condensed form and ruin everything, including the ending.