"To reduce his work to just another special effects-laden action flick is unworthy of it." I know that talking about "reducing" in this context is a figure of speech, but underlying it is a metaphor that doesn't really apply.

The existence of a film does not reduce the book on which it is based. If it was a bad film it would be irrelevant. As a good film it can even augment. In this case I think it is a good film. As for special effects - good special effects cease to register as such. You find yourself not thinking how did they animate that sequence?", but rather "where did they find that troll?"