While the movie is meh as an adaptation, I saw it years before ever reading the book, so long ago in fact that I had to sneak past my parent's bedroom to do it late one saturday evening. It creeped me out as fuck even then, more than any slasher flick. Like it's what got me into alternate history as much as British Warfilms.
EDIT: IT has plenty of eye-rolling stuff, such as the TOTALLY NOT Beatles, but other than that, the production values are fairly good for that sort of thing, especially a TV budget even if it's HBO. Hell, they used 60s vintage vehicles throughout, and as unworkable most of Germania would be IRL as Berlin literally stands on sand, it was very believable.
Re-watched the first 20 minutes or so on the Tube. Excuse me while I watch my favourite scenes from Battle of Britain to wash off the stain.