I never read an issue. I heard that it was an amazing run, did Sim complete his goal of 300 issues with a single writer/artist? I also don't know much about it, but in later years people started to label him a bit of a misogynist.
I only encountered Cerebus twice, in TMNT #8 which was an action-adventure that worked for me; and in Spawn #10 which was kind of a pretentious exploration of the creator/character relationship.
The series went off the rails a bit towards the end ('the end' being the last hundred issues or so), but I would say that for 200 issues, Cerebus was one of the best comics ever produced anywhere, in any language.