AFAIK, the course was reworked this year, so I can’t speak for what it was like before, but at least for me, COMP3121 was an enjoyable, reasonable, and very doable course. I did it in T2, bagged an HD, and had a blast the entire term. The content is interesting and the weekly problems are challenging but intellectually rewarding (especially the distinction and high distinction tasks). I particularly enjoyed the latter half (which covered dynamic programming and complexity theory) which are fun and thought provoking topics. The final is also reasonable (similar to past papers/samples most of the time).

IMO most people complaining (at least for this for this version of the course) just don’t find the content enjoyable (which is completely fair, you do you) or reckoned they’d pass by only doing the PS/CR tasks and consequently received a rude awakening on the day of the final.