no, the material is no problem for me.
what maters to me is:
1. back cover design. I'm not type of people who like to use colorful case, I like the transparent one so when I use my phone, people will know what phone I'm using. And that design is not work for me. I personally more like pattern of the S4 back cover. It feels more elegant to my eyes. And don't say those faux leather in note 3. I like it almost. So if the S5 use those like in note 3. I'll be more attract to s5 rather than z2.
2. the battery. It's already boosted 200 mAh from the s4. That's great but not enough. I own myself a S4. It's pretty durable when use power saving mode. but that's where I hate it. When in power saving mode. When I move from outdoor to an indoor place. The screen is very2 dark and I almost can't see it. I don't know about this mode in S5, or the stamina mode in sony device. If same as in my S4, then I need bigger battery for my next phone so I can use it in full day without those power saving things.
3. As like many other people in xda discuss it about when it's first implemented. knox things. I hate when samsung finally use it. I know it's just a flag, but I didn't know how the regulation about that knox warranty here in my country. And if that knox used as one of main upgrade (like that knox countainer in S4 upgrade from 4.2.2 to 4.3), obviously we here can't use it. And make the upgrade less.. useful I guess. Since phone performance will not dramatically change because the phone still have same component