I downloaded iZone the day it was released to the app store (back in December of 2012, I believe) and I went back to Classic after just a short while.
1) The game is confusing. A lot of things I did not understand how to do, I didn't know where to go, and I never liked the idea of admin-bots, just makes it that more difficult to PM someone for help. I tried towering but that confused me, I never really liked the ideas of "ranks" or whatever (I tried joining a tower guild and the leader said I had to be at least two levels above the default rank or something...and it was the first day.) Also, I didn't know how to even change my rank or level or whatever. I also didn't know how to make money. I asked some people and they told me that you have to win in a survivor or something? I don't know.
2) I have spent money on other servers. Yes, I admit, I have purchased a gralat pack every now and then on classic. And while I am still confused on how exactly you can make money on Zone, I'd rather not spend even more money on a server that is confusing to me.
3) I have friends on Classic. Yes, friends who didn't like iZone either. If I was going to join Zone I would have rather joined it with a friend or someone I'm familiar with to possibly help me along with the game. But nobody wanted to go to zone most likely for the same reasons I posted, and when I tried to make friends on zone someone said "show me your most expensive gun and I'll think about it" so that didn't really work out.
4) Originality. Yes, you have player shops (which tbh are quite dead (no offense to Hadi or Jared)) and those are nice and all, but then you completely rip off Classic's gift system...yeah. I think if you were a little more original with these larger events, you would appeal to more people. Lowering the prices on gifts and allowing someone to gift themselves is a cheap way of attracting players from Classic (we had the same system with more expensive gifts, and you were unable to gift yourself, so of course Zone's system would seem more appealing). You're basically saying "Hey, we have the same gift system as Classic, but our gifts are cheaper AND you can gift yourself!" Yeah, no.
5) Balance. This is more of a preference to me rather than an actual problem, but I never really liked the idea of a player possibly having an advantage over someone in terms of weapons. I know this most likely will never change but the reason I like Classic and never play Zone is because everyone in Classic is balanced. (btw I don't even know what 360 shooting is in terms of gameplay or how it affects zone.)
6) The tileset and the HUD (basically the menu) is unappealing. Just like what everyone else has said, the tileset could be better, and so could the HUD.
7) Better GMAP. I'd like to see different towns/cities/areas/etc. with actual names to go with them. Like Ryan said, Classic has Snowtown, Swamptown, etc. Also, why are a bunch of the hat stores all named Hatz? If you gave them different names it would be easier to remember where a certain hat is. Example:
"Hey, friend, where did you buy your hat?"
"Oh, I got it at Hatz."
"Ok...which one?"
"I don't know, but I know for sure that it was called Hatz."
"But there's a bunch of different Hatz! Do I really need to go look inside all of them?"
A preferable scenario would be:
"Hey, where did you get your hat?"
"Oh, I got it at the Astro Shop."
"Cool, thanks!"