In my mind a rating would consist of some numeric rating (1-5, for instance, perhaps along multiple dimensions, e.g.: quality of documentation, type-safety of interface, performance) for a particular package. The user, date, and current version number should also be recorded.
I think a simple like/star mechanism is better than 5-star rating. Otherwise I, as a package author, feel tempted to make every user happy in fear of bad reviews (which may not necessarily lead to the most consistent or future proof API). Writing high-quality packages is not a popularity contest! Or maybe just integrating GitHub stars is the way to go? If this leads to more stars for Haskell projects on GitHub, this would also help to promote Haskell in the large open source community! Cheers, Simon