The phrase "mediocre reviews" means that something, like a movie or a product, didn't receive very good or outstanding feedback. It suggests that the reviews were average or just okay, but not particularly impressive. Full definition
Most days are filled with mediocre reviews and rejection, often from my cat. (rmfw.org)
I will continue to purchase and feed this to her even though it gets mediocre reviews. (royalcanin.com)
For instance, maybe one credit card issuer you're considering is hailed for its superb customer service, while another receives mediocre reviews for its service. (creditkarma.com)