I've read this paper several times, over the years, and I've never understood why its considered such a landmark. I think it could be losslessly compressed to one paragraph of modest length.
Many people (e.g., Daniel Dennett, myself) think it's a terrible paper that has done a huge amount of damage. Unfortunately, that too makes it a landmark. Likewise for Searle's Chinese Room argument and Chalmers' "hard problem" as discussed in "The Conscious Mind" and elsewhere.