I haven't read it, but I've heard the Forrest Gump movie is much better than the novel.

Buffy

"The Manchurian Candidate" isn't a great book.

They Live.

The Thing but not The Thing From Another World.

Most things based on the work of PKD.

A lot of Lovecraft adaptations have to be a bit loose (because his stories tend not to lend themselves to films and he wasn't a good person) and are all the better for it - Re-animator, From Beyond, The Color Out of Space, Dagon, etc. plus quite a few fan films.

Flash Gordon film.

The first two Blade films - they struggle to make great Blade comics.

The Legion TV series.

Haven't read the comics, but everyone says that The Boys tv show is way better

I think the TV series of Station Eleven is better than the book. Not that the book is bad at all, but the show is something else.

Manhunter (1986)

In-A-Gadda-Da-Vida, baby.

The Ten Commandments

I think the anime adaptation of Frieren: Beyond Journey’s End was genuinely better than the manga. Which is saying something, because the manga was already pretty damn good.

A Very Brady Sequel.

Yorkshire puddings.