"Am I supposed to hate Zack?" is an excellent question. Really.
So we've got this guy who is generally happy-go-lucky, competitive, strong-willed, looking to help anybody in need, and on top of that incredibly attractive and charming. A typical hero starter pack. I mean, what's not to like? But, I thought, there must be something, at least some bits and pieces, which would elicit some healthy criticism.
#1 I feel like criticizing Zack for not keeping in touch with his parents. They must have been worried sick, but eventually gave up on the idea to see their son again. But this is my rational adult ego speaking. Who isn't rebellious in their teens? Besides, his life in Shinra was eventful enough to keep him busy and sort of oblivious anyway. But it still doesn't justify him enough.
#2 Zack never answers e-mails?! Okay, okay, my assumption is that he does, but the game never shows it because that would take additional screentime and would probably be unnecessary for the plot progression. I don't expect the Metal Gear Solid level of interaction, but I'd still love to see at least a few replies to Kunsel's, Cissnei's, or Cloud's messages.
...aaand whoops I've run out of ideas.