A good offense is better than the sum of its parts. With the reported deal for Randy Moss, the Minnesota Vikings are attempting to revitalize a passing offense that fell from fourth in DVOA a year ago to a stunning 30th this year. If you take a statistical look at what's changed about the Vikings offense, though, it's hard to imagine Moss serving as more than an extraneous part of a flawed passing game.
To succeed, a great passing offense needs receivers who can run every route on the route tree effectively. While some offenses (Houston) get by with one dominant receiver who can do anything you ask him to, virtually every great passing offense has a mix of receivers whose strengths play off the other guys in the mix.