The CA is almost unbearable (LR4 does a decent job of removing it) and I find that mine offers poor contrast and a blue-ish color temperature compared to my other lenses.
But more than anything, it's the CA that I utterly hate.
Out of curiosity (since this is a 6D thread) have you found the 6D's CA Correction to work? I presume it would be for JPEG, unclear if the correction data is available in RAW. Obviously the contract and color temp wouldn't be corrected by this, but wondering if you had experience with that feature in the 6D itself?