The look is the ONLY axis where Guzman is a good fit. Very few of the critiques I see are about looks, and yet the responses always seem to bring up looks as if they can debunk the problems by pointing out the non-problem.

He's not dynamic enough.

The biggest problem is that, he and Morticia look like they're faking it. Past iterations have always looked like they couldn't wait to be alone together. These two look like as soon as they're alone they can change into sweats and go to separate rooms to relax.

It's also tricky that G&M have to do the "concerned parent" thing a few times. They skate awfully close to the thin ice of being "normal parents", threatening to put some of the core Addams on the wrong side of the "normal / weird" divide.

As others note, those latter two problems are writing and direction, not casting.