I've never understood the "You shouldn't review this game unless you already like the series/genre" mentality.
I like those reviews the best because they're informative. One of the really really old game magazines back in the day used to have a panel of reviewers who each was interested in a particular kind of game/genre. Here's the opinion of the reviewer who likes RPGs and here's the opinion of the reviewer that likes side-scrollers...etc. Each reviewer told a different story about the game based on their own interests.
You could also take a little test to see which reviewer's personality matched you the best and thus which score would be closest to what you'd give it yourself. I thought that was pretty neat back then.