These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Screwtape Letters
Big Lipped Alligator Moment: There's a random scene in the play where Toadpipe brandishes knives at the audience while creepy music plays. Why she does this is never explained, not even from a Doylist perspective, since the set isn't changed during that scene, and only purpose seems to be to set up the knives for the final scene.
I think Screwtape said something about getting ready to "receive the patient". I guess it was to showcase exactly what was in store for either the corrupted mortal or the hapless tempter that failed to bring him in.
Creator Backlash: A relatively mild example. Lewis said in the foreword of later editions that while Screwtape was one of the easiest things he ever wrote, it was also the least enjoyable. As he put it, it caused a kind of moral cramp, forcing himself into a demonic mindset. He also resented it for not being something he felt he wasn't skilled enough to write - Screwtape's advice balanced by angelic advice from Heaven. For these reasons, he never wrote a sequel, though he did write a toast (a scathing criticism of the American educational system at the time and its resulting Tall Poppy Syndrome) in Screwtape's voice.
Evil Is Cool: Subverting this is pretty much the whole point. Not only is Screwtape himself a stuck-up member of Hell's middle management and a cranky Jerkass with no sense of humor, but he gives tips to Wormwood on how to minimize how much The Patient can enjoy sinning.