Will is busy every winter preparing for the ACPT in February, but he will respond to puzzles somewhat sequentially when he is able to make time. And, yes, he looks at every puzzle himself. Over the years he gets more and more submissions, so he has less time to point out features on each puzzle. He used to return submissions by mail with a few annotations: now he usually summarizes the reasons for a reject in an Email (sent out by his assistant Paula Gamache) -- because he doesn't have the time for more elaborate input anymore. (Or in the case of an acceptance, he'll point out what he particularly liked).
In my above paragraph, I say "somewhat sequentially" because I think he gives every puzzle an initial glance in the order in which they arrive on his desk. But, some decisions are faster than others because of various factors: If his puzzle inventory for a particular day of the week is high, then he might not decide right away. Or, if a puzzle does something out of the ordinary, he may have to think about it for a while -- particularly if he has to figure out how to apply a fix to it down the road. If a puzzle is thematically flawed, he may be able to reply sooner -- with a rejection: but he is also careful not to discourage beginners. If the fill is flawed, he may decide to conditionally accept it -- but he first has to assess whether he can fix it himself (up to 15%) or whether the constructor should fix some/all of it. So... if he isn't able to make an assessment on first glance, he'll need to make a second pass -- and that's why responses don't always come back in the order in which we submitted them. But one things for sure: he doesn't play favorites; All constructors have an equal shot and the decision is based on the quality of our work.