We've just released the first version of a new tool to compare the installs, uninstalls, retention, ratings, and more.
It uses the data that Google makes available for download to every developer. After importing data, you can easily see trends of your apps over time and compare them to each other.
This is a first beta release, if you're interested in trying it out, head to https://www.appgenius.org/
If you have any feedback, please let us know, or discuss in this thread!