He's one of the worlds best kicking 10s and, tackle technique aside, one of the best in D, and he certainly makes a difference to England when he's on the field. Room for improvement certainly but to my eye he is improving year on year.
This simply isn't true though (the bolded - his positive attitude certainly does seem to make a difference to England; and yes, he IS improving year on year - he's currently "competent but prosiac with occassional good days" as an international, at either FH or IC).
He was a solid 80% kicker, so decent, international quality, but not close to world class; currently though, his kicking stats have dropped (or they had last time I looked). It's just a run of bad form there, but even before, his kicking was no better than Ford, Cipriani, Smith etc. His kicking from hand however, has always been inferior.
As for his defence - aside from his tackle technique (that's a hell of an "aside") is undisciplined. He's finally improving, but he still has difficulty holding his place in the line. As an individual tackler, he's fine (aside from going high and not using his arms); but as part of a team he still too often runs out of the line leaving a dog-leg behind him. Sarries make a virtue out of it by throwing him at the FH's outside shoulder, pressuring the pass/kick or turning him back into the big guys. This simply doesn't work at international level, or from the IC position - but he keeps doing it anyway. As said, he's getting better here as well, but he's far from being a good defender - people just think he is because he's rarely loses ground in head-on collisions. Compared to Ford (for example) he has terrible technique, a poor tackle success rate and is often in completely the wrong place to make a tackle in the first place, leaving a hole in the defensive line.
It's part of the myth of Farrell that so annoys so many people, and encourages OTT criticisms of him in response the the OTT praise he usually receives.
Sorry - I feel the need to expand; I generally try not to.
I think it's to do with England's hang-ups and inability to see the present not the past. Farrel bases his game on kicking, and defence; St Jonny based his game on kicking and defence => Therefore Farrel in the second coming of St Jonny (who was the second coming of Squeaky Rob) => All Hail St Owen.
Ford bases his game on bakk-in-hand play, gives up ground in the tackle and has had 1-2 matches where he got the yips from the kicking tee - therefore he must be the second coming of Charlie Hodgson (who in turn was the second coming of Mike Catt the FH) - the enemies of Twickenham => All Condemn the Demonspawn.
They are absolutely terrible comparisons, but they seem to be the ones made, and the only reason I can find for the lauding of Faz and the distrust of Ford.