Please do yourself a favor and skip the adaptations by James Blish, they're awful.
Can't agree there. They are definitely products of their time, and very brief by today's standards of novelization, but the early Blish ST stories are often based on early draft scripts, have tantalizing connections to other Blish SF tales, and were originally enjoyed by both adults and children - and that makes them important, fascinating, nostalgic and certainly not-awful. (Or maybe it makes them full of awe?)
Once I started on the Blish adaptations (in 1980), I couldn't put them down till all episodes had been devoured.
As a school librarian and ST fan, I've met numerous adults who taught themselves to read as kids with Blish TOS novelization collections (and Batman comics), in a time when home video was beyond the public's comprehension and everyone relied on the flukiness of a TV network to repeat a favourite episode that had only ever aired once before.