It might just take a plugin that adds a rating functionality to threads to make this a workable system with the existing forums.
So each thread constitutes a review, members can rate a thread (which in effect is rating the item being reviewed in it). These ratings would need to be displayed alongside the thread title. You'd need new options to re-sort the threads by rating. Additional screens to view the rated threads across all the forums, say in a top 10 or top 50. Thread rating would need to refuse members who had already rated it.
And options to specify which forums to have the ratings enabled, which usergroups can rate, display who rated, delete selected ratings, which usergroups can see who rated etc.
I think I would prefer a review system like that, with forum threads being reviews (since that is the posting and replying options already taken care of).