Here's the basic issue.
ESPN's QBR and Football Outsider's DVOA are arguably better measures than passer rating.
But both of them suffer from the flaw that they are not transparent: I can't "play with the numbers" and figure out what Brady's DVOA would be if, say, Amendola had taken that 57-yard pass to the house.
So there's always the pull between limitations versus transparency, and simplicity versus completeness.
Of course it also means we'll likely never run out of stats to argue over.
[ObPostscript: What PFF puts out are not really "stats" in my book.]
QBR is clearly driven by narrative, however. The 'situational adjustment' and 'clutch factor' is silly and adding a subjective adjustment to numbers (on top of that, numbers we don't know about) allows you to skew the result in whatever way you want. The classic ESPN narrative is that Tony Romo is a choker, therefore we can adjust Romo's QBR in any way we want to play into the story we want to tell. It's narrative with meaningless numbers made up to drive the story ESPN wants to tell.
On the other hand, DVOA is more complicated, but there is a formula behind it. If a play on X down from X distance goes for X yards it is successful/unsuccessful, and this holds universally. So while the determination of success is subjective, the fact that this applies universally reduces bias, while QBR is biased because the determination of 'clutch factor' and 'situational factor' are made on a case-by-case basis with a human applying a constant discount or multiplier to each case (this may not be true, but I tend to have a very low opinion of ESPN that I think is rather widely shared among knowledgeable sports fans).
It's complicated statistical work, but you could - if you had the inclination and enough statistical chops - probably discover what the adjustment to a team or passer's DVOA would be if a play went for 50 rather than 3 yards as long as you had access to the play-by-play dataset that FO uses and their algorithm for determining play success.
There's a subtle but really important methodological difference there. Passer rating is largely useless not because it's methodologically unsound, but because it's conceptually unsound. It's like talking about today's prices in 1940 dollars. QBR is methodologically unsound. DVOA isn't simple or transparent for a non-stathead (I'm a demographer by trade, I do stats for a living), but it's the best you get in the middle.
I think that this "Bruschi index" is actually quite useful for conceptualizing how good a defense is - I'm taking issue with the fact that ESPN acts like it's groundbreaking to average a bunch of rankings together. Heck, their own fantasy football writers have been doing that for years!
As for PFF (and KC Joyner, who did this kind of stuff before PFF), it's just as bad as QBR. It's almost entirely subjective, riddled with bias, and there's very little explanation of the methodology. I think it's entertaining to read, but FO is the only real methodologically sound advanced NFL metrics site on the web.
I'm also biased because FO posted a column I guest wrote last spring on "the 10 yard ditch" (which, anecdotally, we saw the Patriots fail to score TDs on 1st and Goal from the 10 this past Sunday twice).
