"Lukewarm reviews" means that something, like a movie or a book, received only moderate or mild criticism or praise. It suggests that the item was neither exceptionally good nor exceptionally bad, just average or mediocre. Full definition
Sure, it's only received lukewarm reviews, but the presentation and atmosphere are absolutely incredible, and in my opinion even the gameplay is pretty fun. (ps3attitude.com)
The game wasn't terrible, but it turned out be another example of a mediocre launch title, getting mostly lukewarm reviews from critics. (slashgear.com)
The PC release has received lukewarm reviews and there have been numerous issues regarding bugs and exploits. (gamingenthusiast.net)