What is concerning, is the very real holes in coverage adjacent to the J curve SSR envelope.
That ... and the exemptions for RPT aircraft to have unserviceable ADS for a few days.
Oh ... and the glitch in the 787 that provides the occasional incorrect position information.
And then there's the VFR traffic ...
But apart from the holes in coverage, the exemptions, the glitches and the invisible VFR aircraft, what has ADS-B ever not delivered for us?