This plugin is fantastic. Already, because we were able to implement this voting feature, the page on our site with the image voting has drawn more traffic than any other page in the history of the site.
Although this plugin is dependent on NextGen Galleries, the author of this plugin goes out of his way to ensure compatibility in a VERY timely fashion. I highly recommend supporting the author for continued progress of this plugin!
Buy the Pro Version... It's worth every cent!