Are there any especially inconsistent authors that have the capacity for really great stories but have sometimes either phoned it in or just totally missed the mark?
A couple off the top of my head with particularly big gulfs in quality:
Robert McCammon:
Swan Song is absolutely excellent if a little cliche-ridden.
Stinger is one of the most derivative and repetitive books I've ever read.
James Herbert (even in the same series):
Haunted is a classic haunting story, especially for its time. It feels predictable now but for the 80s, very solid.
Ash the book that is 2 sequels later than it is absolutely awful. A rambling, non-scary, unfocussed mess with a baffling reveal.
by Skeet_fighter