Film ones not so much, but Doctor Who does novelise their modern episodes especially since every Classic Who episode has been novelised. Most of them are fairly bare-bones retellings of the plot but the best expand and reimagine the story. The very best in that regard is absolutely Steven Moffat’s Day of the Doctor.
At the moment, the new episodes are getting their novelisations released digitally the Monday after they air with physical copies coming in January. It’s nearly the shortest turnaround time for an episode novelisation, only beaten by the novelisation for The Five Doctors coming out before the episode.
I would say Good Omens, the book is fantastic but the TV series loses barely any jokes and feels like a more complete story what with the new ending. I’m not counting Series 2 in this as I’d say it’s worse than the original series that adapted the book and it’s only a bridge to Series 3 that will be the planned sequel to Good Omens.