I thinking building on this would really up the usefulness of your site immensely, because people want to know what's out there when they're looking for tools. Rating is secondary to someone looking for tools. Instead, they need to know what tools exist. Building out the categories more is a suggestion, as would be providing your own content (editorial) on how well apps in the same category work compared to each other. For example, if you're looking for a commenting system for your blog, what are the pros and cons of the major offerings. I understand this might run into a problem of what is a web app and what isn't, but people love to have someone else do the work of finding them a solution. That involves more than a one line description and a rating.
Rating is good to eliminate the lowest bottom feeders, but it doesn't help you choose between two five-star programs. Original editorial content helps people by providing more information, as will user comments of course once you get a mass of users.