I’ve heard this good writing advice before (I don’t always follow it, to my detriment), in words like “Your prose should be as invisible as a pane of clear glass.” But I’ve never heard it put quite like this.
Having beautiful imagery, vibrant vocabulary, and full sensory-immersion is a good exercise for authors, but four or five hundred pages of it is too much. It’s tiring for the reader to process. Ideally, for most authors, your words should become invisible, and the story should take center stage. If the reader is continually awed by your linguistic gymnastics, your prose is competing with the story for the reader’s attention.
(Driven to desperation by the mismatch between the 13-hour plane flight and my 5-hour laptop battery, I read a dragon fantasy book by Patricia Briggs. I enjoyed it more than I like to admit.)