I've been pretty pleased with my ZU. The one thing that I thought I would have a problem with was the lack of a flash. To my surprise, I don't miss it at all. Phone flashes produce sucky pictures. If you are in a position to use a phone flash, you could just use it without a flash and it won't make it any less bad. I do, however, miss having a flash to use as a flashlight. That is seriously the only thing that I miss about not having a flash. I do hope for a better camera unit on the ZU2.
Another thing that surprised me is that I actually do value the waterproofing. I didn't think I would care much about it, but it's actually been pretty great to have a phone that I am not worried about getting a little wet. I spent the last few days with the missus in a nice hotel with a big hot tub, and I had no problems bringing my ZU in the tub to read. A non-waterprooof phone I wouldn't have dared.
The speaker is a little lame, but I see that as a consequence of being waterproof. If the ZU2 had stereo speakers that would be cool, though. Also they REALLY need to improve the quality of the earpiece speaker. When I am talking to other people they inevitably sound mushy and quiet. I don't like that at all- it's probably my biggest gripe about the phone.
Another gripe I have is that the oleophobic coating rubs right off the phone pretty quickly. I haven't had mine for too long, but it is easy to see where I have rubbed the oleophobic coating off, because fingerprints show up like crazy, and water spreads out in the worn-out spots rather than beading up. I would like for them to do something about that in the ZU2.
I have no problem with the battery. Sure, I'd love to see a 4000 mAH battery in the next ZU, even if they had to make it a little thicker (7.5mm for example), but either way it's not a big deal-breaker for me.
I also would not want to go any bigger than the current ZU in physical size. If they can fit a bigger screen in the same size, or maybe even give us a slightly smaller size with the same size screen, that's great. But if the physical dimensions get much bigger I'm afraid I would have to upgrade to a different phone.
All in all, I am quite happy with my ZU, and I think it beats all current phones on the market for my use case. If the ZU2 improves on a few things that I have mentioned then I will snap it up, no questions asked.