According to this topic:
You have to be a member of, I'm assuming, one of the 5 main guilds on BYOND to review a game?
I can see this being sensible for the reviews that show directly on the hub pages. But anyone who wants to should be able to review games, or at least all members should be able to. There could just be a link from hubs that takes you to "All Reviews" regardless of what guild, if any, the review was submitted to.
If nothing else, there should at least be an official Reviews guild that all games can have reviews submitted to by anyone (or members only).
Since the rating system on reviews seems to be back, the page displaying all of the reviews could show an overall average of scores from official reviews, player reviews, and a combined average from both.
I've seen a lot of reviews popping up on hubs and then mysteriously being gone within the next few days. I'm not sure if this is from the writer deleting them, or from a poorly designed submission/review of reviews system, but it seems rather strange either way.
EDIT: On a somewhat related note, if you delete a hub entry, and then remake one with the same name, any reviews that were made on it will be unassociated, but still exist.