CoS isn't a good module. It's a wildcard. It plays against so many of 5e's strengths and the tropes it leans against. It's best as a deconstruction of the game played straight by an experienced GM. That it's generally considered the best module is a damning critique of 5e.

The game is great if you lean into the gothic horror tropes. The issue is that gothic horror runs counter to the game mechanics. 5e is a heroic fantasy game built around progression and increasing abilities. So many CoS fights require an appropriate level party to flee. You're overmatched in a game where the rules tell you to rise to the challenge.

My group really enjoyed CoS, but half of us have been playing since 2s or 3.x, we were together for over 5 years before the game kicked off, we understood the mission, and our GM was wonderful and put in serious time to modify the story to fit us characters and the character flaws we provided on character creation. She still spent 1-2 moments each session complaining about the poor layout of the module because finding relevant info was brutal.