Almost completely a suggestion of whimsy rather than being realistic:
There may be a call for "halo effect" and reviewer bias checkboxes like:
Reviewer admits to being a fan of the author/dislikes the author
Reviewer admits to having judgement significantly influenced by nostalgia
Reviewer admits to what they see as being a cool factor of concept of the product (e.g. "big, big dungeon!") significantly affecting their judgement of the actual execution of said product
Reviewer admits to what they see as being a poor concept of product affecting their judgement of the actual execution of said product.
Reviewer admits to judging product more harshly or more favourably because it's published by WotC/not published by WotC
Reviewer admits to being a fan of/disliker of cthulhu elements
Reviewer admits to being a fan of/disliker of psionics
Reviewer admits to being a fan of/disliker of the lower planes
Reviewer admits to being a fan of/disliker of low magic and "grim n gritty"
Reviewer admits to being a fan of/disliker of high magic and high fantasy
Reviewer admits to being a fan/disliker of settings X, Y and Z
Reviewer admits to preferring crunch over fluff
Reviewer admits to preferring fluff over crunch
Reviewer admits to only having done review to bump up the rating of said product
etc. etc.
That way you could match your own preferences and biases to those of the reviewer, and decide that because their priorities don't match yours, to take their words with a grain of salt or more. Reviewers don't like to think of themselves as being biased by stuff like nostalgia or being a fan of the author, and it's pretty easy to tell when they are, but some of them hide it pretty well and you end up buying something with dodgy execution based on their halo effected or "I'm a fanboy/hater of X so I'll flagwave for it/throw mud at it" reviews. Caveat emptor.
Altogether, that's way too many checkboxes. Perhaps reviews could have an "admitted reviewer bias" section instead. But then again, most of us are blind to our own biases, or see them as "being objective", so the above suggestions are probably pointless.
Perhaps the more biases a reviewer admits, the more their review is respected. It would cut down the amount of reading time of multiple reviews as part of "getting to know the reviewer" and trial and error in buying products they recommend to see how your preferences and biases match those of the reviewer.