I won't lie, I want more Zack, because he felt barely brushed in FFVII when he was such a major character to both Cloud and Aerith. It's only fair (haha) that we'd get more of him in the game through flashbacks and whatnot.
I might be giving the game too much credit, but I think that Zack being so disregarded is sort of geniously heartbreaking.
I recently got to watch a friend play the game for the first time. He had Aeris in his party when he got to Gongaga, so he got that lil scene with Zack's parents. Then in the middle of the scene he started inputting commands into Twitch Plays Pokemon and I got REALLY MAD. I was like, pay attention, this is important, Zack is so important. Why aren't you crying right now.
I pretty much cry over anything regarding Zack. I think a large part of that is, though, that you are sort of inclined to overlook him at first. Then when you find out how important he was, and how good of guy he was, you already know he's dead, and that's so painful.
Though, I would like to see Cloud be a bit more apologetic about stealing Zack's life. Maybe tell the rest of the team a bit about the guy. Keep him alive in our memories, so to speak.
Also, I'm the kind of person that is constantly revisiting old sections of map at any possible point of state change. I saw the Shinra mansion flashback on my first game. I loooove exploring and stumbling into things like that.