I've flown J on AA DFW-NRT and back four times, the most recent in March. It doesn't even compare to JAL service (I've flown NRT-SIN and back, most recently in March). If you have any chance to change carriers to JAL metal, I would do so. I have no experience wtih new business class on AA.
That said, it's certainly better to fly J than Y transpacific.
My employer didn't pay for business class for flights less than 8 hrs so I was always happy for the upgrade.