Well, after a few hours of use I am very content. What stands out most to me is the speed. The iPhone 5 is blazingly fast. Everything loads in a snap, there is no lag that I can see in any of my programs, and no delays waiting for a tap to register. For anyone who currently owns a 4 or earlier (as I did), this will be a major upgrade.
The size of the screen is still enough of a novelty that it surprises and delights me every time an app takes full advantage of it. Remarkably, almost every app I use daily already has: Kindle, Instapaper, Reeder, Tweetbot, Alien Blue, Articles, Downcast. I expect nearly every popular app to support the new resolution within a couple weeks. Reading is greatly improved as a result, and it's much easier to scan information at a glance in your email or calendar.
It is remarkable how lightweight and thin the phone is. I hardly notice I have it on me. I usually carry my phone in the breast pocket of my suit jacket and had to check it was there a few times just to be sure. That makes it all the nicer to hold for long periods of time, great for reading novels. Huge improvement.
A note about the maps: this is a mixed bag. After a fair bit of use, I'm convinced the problem is not the app, it's the data. In some ways, Apple's new app surpasses the old. The use of vectors instead of static images means zooming in and out is incredibly fast and smooth. 3D flyover is largely well-done (in my city, anyway) and visually impressive. Integration with Yelp is great for looking at restaurants nearby. And there are no ads or sponsored results.
However, the app can't even find my home unless I tell it the city and the exact postal code (apparently there are three other streets with the same name within a certain radius). Transit directions are nonexistent and I couldn't get any third-party apps to work. A great deal of data that was overlaid onto Google maps (store names, buildings, landmarks) is gone. It's frustrating to say the least. Hopefully they will get better in a big hurry, because the platform is quite nice.
If anyone has any questions, feel free to ask.