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The only book adaptation from Michael Crichton's works which stayed true to the main plot elements in the book was Sphere. Though Jurassic Park was a good movie, they strayed significantly from the story in the book where things go from good to bad, back to good, then to worse instead of from good to bad to worse. As a result, the second movie had to create whole scenes in order to connect from the first movie, and they were bad.
The Andromeda Strain (original) was also very faithful, but drawn out for a screen adaptation. The 13th Warrior was a decent adaptation taken from the Beowulf/Grendal story, but not great. Haven't seen Timeline so don't know there.

Worst ever adaptation: Congo. Between complete remakes of all the major characters and the animatronic apes, this one rates on my list of worst films of all time list. It really deserves a remake with modern technology, but most of all has to maintain the characterization given in the novels.