I agree with the concept that rankings help you sort out some of the mediocre pins from the good ones in terms of seeking out the games you will like, but whether or not a pin is "good" is very subjective.
Some people like short players, some people like playing long games. Some people like open playfields and others like them full of ramps and gadgets. There's no "right" or "wrong" answer.
When you add that to the fact that people manipulate the rankings for invalid reasons (they want the pins they own to be ranked higher, they want to sell a game and therefore want the ranking to increase, they unfairly give low ranks to games they haven't really played enought to rank)you end up with an unreliable data pool anyway.
The pinball players I talk to in the real world never seem to have problem with the concept of each person having equally valid reasons for liking certain pins the best. I think the collector market tends to get lost in the ether sometimes.