Honestly? I don't know that Matt has as much fun playing (in this campaign) as he had GMing CR1 through 3.
Whether it's the way Brennan does things, or the tonality of the campaign (both of which seem very different), or just sitting on the other side of the screen for such a long time (way longer than during Aabria GMing) - I dunno.
It's all gut-feeling anyway.