All the review aggregators are useful to some degree, you just have to tailor them to your own tastes.
If I see a random monster-horror film on Prime, with a limited number of reviews on RT and MC, I'll go by the IMDB, and adjust the score according to my preferences. As I enjoy even the schlokiest of monster films, a 5 and above on IMDB is worth my time.
If it's some dense, complex film, I'm less likely to go by the IMDB score, and instead go by the critic average, with a preference for critics with similar tastes. For instance, Aleksei German's Hard to be a God has a 6.7 on IMDB, but a 9.1 critic average on RT. In such cases, I'll use the critic average to decide whether it's worth my time.
(It was.)