For books in the neighbourhood of Epic Fantasy and published in the last 5 to 10 years I have observed a close correlation between number of GR ratings and sales.
For books in other genres and for books published pre-2007 this relationship will get sketchy. My impression is that the formula for sales in English (multiply number of GR ratings by 8) will start to underestimate sales more and more as the publication date retreats into the past. Additionally children's books (as opposed to YA) are heavily underestimated by the formula as children are less likely to use Goodreads than adults.
Anyway. Here are the numbers of GR ratings for a selection of fantasy books often discussed in places where my books are discussed.
The interest in various forums skews in different directions, so in some places you might come away with the impression that any one of these was really killing it in terms of sales and "dominating" the genre.
But when we add in some of the really heavy hitters also discussed in those locales...