There's little I can say that hasn't been said already. Is it a surprise that his "done for good" statement didn't stick? No. Will his addition make the Vikings a better team? Probably. At the end of the day, regardless of his shortcomings, you'd expect Brett Favre to be an upgrade over Tarvaris Jackson and Sage Rosenfels, especially if (an admittedly big if) B-Favre's able to accept his role as a *gasp* game manager and part-time gunslinger. Comparison's to Elway's late career Super Bowl years (as a decision maker in service of the running game) are appropriate.
After the late season fades he's had the past two seasons (his last with the Packers and only with the Jets), there's every reason to expect one this season. Not for nothing, I'm pretty pissed the both the Packers/Vikings games pop up in the first half of the schedule....
While I'm definitely excited by the prospect of being on the other end of a patented late game, back breaking Brett Favre interception, I'm equally dreading the prospect of watching Favre, aided by Adrian Purple Jesus Peterson picking apart the Packers' defense, a distinct possibility with a new defense being broken in this year.
While I think that all the "are the Vikings the team to beat?" talk is laughably premature, I will say that, between an imposing Minnesota team, Atlanta, Philadelphia, the Giants, Arizona, New Orleans, and an improved Green Bay team, the NFC picture is about as interesting as it's ever been.