I got some enjoyment out of every book, even the unreadable later ones that are half 8-point gibberish text. But I would say that for the average reader, Jaka's Story is a good stopping point. For the more impatient reader, just High Society is plenty.
Throughout the series, I enjoy the various celebrity cameos, especially the cameos of comic book creators. I enjoy when Sim and Gerhard do interesting panel arrangements and when they swing the "camera" around in 360-degree arcs for page after page, even when the action portrayed in those panels is kinda dull by some standards.
I love the issues where Cerebus is dreaming, or flying through space. I love the issue where gunpowder is invented and a cannon is fired off for the first time in history. I love the banter between characters.
Cerebus for me is like an old crotchety friend, who is fun to hang out with now and then. But I can't subject myself to its toxic world view too often, or it will make my life miserable. For the last hundred issues or so, I gave up reading the monthly issues, because once a month was too often. A TPB collection once every other year was just about right.
Given all that, its hard to recommend it to anyone in other than small doses.