His footwork is bad, his decision-making his bad, his handling of the NYC pressure is bad, the OC is not great, etc. etc.
BUT...one of the problems he's got is that the Jets are actually good. If the D was terrible and they didn't have a realistic chance to make the playoffs, no one would care. This would be a footnote in the season---like it is in Jacksonville, Houston or any other city with a young QB playing poorly--but the Jets have a top 3 D in the NFL. They clearly have enough weapons and enough good OL play to win games and make the playoffs. That's what is making this situation worse. That's why the fans and media are so fired up. They're absolutely desperate for a winner and they feel like the team is close.
The problem is that the team developed faster than Zach. I wish he'd had 3 years to watch, but that rarely happens anymore.