I used a Z10 for the past week, to certify it for use for our employees at work.
I'll echo most of what has already been said here. I *really* like the hardware. Solid device, one of the better feeling I've held in a while, love that it isn't too big. For all the knocks that RIM gets sometimes, they do have a history of some great hardware. the Bold 9900 remains my favorite piece of phone hardware ever (pity about the OS on it).
As it comes tot he software, BB10 is solid. There are some things that can be worked on, but it is solid. The messaging hub needs some work as it is very easy for it to get out of hand with 2 twitter accounts, 3 email accounts, Facebook, etc all attached, but I really like the idea. But overall I do like the operating system.
That being said, for anyone who is perfectly happy with the iOS, Android, or even Windows Phone platforms, there is absolutely zero reason to switch to BB10. I'll say say again, BB10 is pretty solid, and there is nothing really wrong with it, I just feel that there isn't anything it does remarkably better than iOS or Android to warrant switching ecosystems. IF you're not really invested in any of the major OS's, especially when it comes to apps, sure there may be a reason to switch, but I've been on Android for 3 years for my personal phone and Windows Phone for a year as my work phone, and I don't feel any want to switch.