I recently watched the Amazon Prime series Good Omens, an adaptation of the brilliantly funny book by Terry Pratchett and Neil Gaiman. I very much enjoyed it, but I felt as if it would be much less enjoyable if I weren't familiar with the book. It is very faithful, even to the point of sometimes missing some of the advantages of television translation.
For instance, I think the series would have been stronger if they had removed the "God" narration and interwoven scenes to fill in the same information with less voice-over info-dump and more character interaction. Some of the jokes probably would have been lost, but others could have been placed into the mouths of characters and been the better for timing and facial expression. This might have required some change in the beats and pacing, but making the series an episode longer wouldn't have outlived its welcome.
I would also have loved to see a bit more of the Four Horsemen, though I know that none of their scenes advanced the plot as such. It would have strengthened the scene where they faced off with the four children (which could have played out a little longer). I also feel as if there might have been a way to better integrate Shadwell's presence. It was kooky even in the novel, but in the TV series, it feels somewhat off-sides and random, not fully part of the main narrative.
The show also may represent a taxing entry point for a mainstream viewer, someone who doesn't have the suspension of disbelief required by regular SF/F consumption. That bit, though, I wouldn't change in the slightest. Good Omens is delightfully wacky, and diluting that craziness would have been a crime.