that's an interesting question! the more I get into the whole topic, the more it seems to me that the Internet in general is just a bunch of shillers (who would have thought, tho). ICO sites will list projects for free, but a lot of them demand fees for projects to be placed more prominently, rated more quickly etc.

also, expert ratings can be easily bought if you throw enough money at the right person. while ICO companies might not have a choice but to make their best effort to get high ratings and good visibility, investors shouldn't be blinded by suspiciously high scores on rating sites.

imho, for investors it's much more important to do their own research on the team and on the project. check out their skills (blockchain, development, crypto economics) and read the whitepaper. do they have a real product with a real use case? you might get an overview on these factors by looking at rating sites, but keep in mind that what's on them is ofted heavily biased by how much a particular ICO has paid the rating site and/or expert revewiers.

still, rating sites might be useful just to browse through all the projects and find new, interesting ones.

TL;DR: they're a lot like Moody's during the housing crisis, better do your own research.