I agree with others that in the larger sense the answer is "everything" because as a 3rd year player, his development is barely underway.

However for me the most obvious aspects of his game are that his accuracy drops like a rock when he's under pressure. And when he's on the run, his accuracy also drops but he also tends to kind of give up on the play. He runs with his fingers crossed that somehow, someway somebody might get open but seems equally satisfied to just throw the ball well out of bounds.

In other words: playmaking versus merely "running the offense". I think some of this is because he was instructed to play it that way rather than asking him to do too much. I imagine McVay will loosen the leash a bit this next season.