There are an incredible amount of potential pitfalls in a review system. And in fact, the one currently in place, the 1-5 star rating system is imminently abusable. That quality would be easily shared with any other proposition, and frankly, not likely to be helpful. What little utility they have is covered by the comments section. Games with a disabled comment section are usually doing so for good reason, and if not, simply avoid them.
The extent to which I would feel comfortable exploring a review system is this outline:
Reviews can be left independent of the comments, and cannot be disabled. Devs and users alike can report reviews, though developer input is placed on a fast-track so as to make sure a developer can get abusive reviews removed post-haste. These are, in essence, a text post. There is no built-in rating system, no stars or thumbs up or down. Thus they have no sway in discoverability. There is a minimum word count (fairly low) to prevent people from useless commentary like "bad game" or "hella fun." Separate from the review system, you can recommend a game. This adds the game to an auto-generated public collection, so it can be shown on a profile page, and an optional search feature would let you search for games with the most recommendations first. There is no "thumbs down" or equivalent, to avoid abuse, review bombing, and brigading.