If one stops to ponder what would make an individual want to rate their landlord on a "RateMyLandlord" kind of site, then the answer is pretty simple: hatred. The biggest reason for people to write such a review is to complain. Usually, the complaints people write stem from issues related to their inability / lack of desire to pay their rent on time.
Landlords hate not getting paid. Especially in major cities, where regulations basically annihilate their ability to operate in an honest and competitive way without significant impact on their financials. Getting their monthly rent on time is really the only way they can turn any kind of profit on their business.
My income is higher than it has to be for the place I rent here in Brooklyn. But I get charged far below market rents. Why? Because I pay my rent every month on time without hassle. Because I don't wreck my apartment, don't need many repairs, and don't bother my neighbors. So even though I could afford to pay the market rate, I am a 'good' tenant, so I pay the so-called "preferential" rent, which is almost $400 per month cheaper than the rent cap instituted by NYC's horrid rent control laws.
That's right. My landlord could actually charge me more, but he doesn't, because I'm not a shithead. What am I supposed to write in my RateMyLandlord review? That I am a good tenant and get charged lower rent than everyone else? There goes all of my reward for being a decent person.
I don't see any way for such a site to work without damaging reputations or ruining nice arrangements tenants already have with their landlords.