I just had the chance to play with the larger 5.5-inch iPhone 6 Plus, and while it's nothing surprising after all the leaks, it's still a fascinating phone. It's right in the middle of the familiar iPhone experience and the iPad; enough so that it's hard to see why anyone would want an iPad mini if they have this larger iPhone.
If you've seen the leaks, you already have a good understanding of what this larger iPhone looks like, but in person it's not at all what you'd expect.
First off, it's much smaller in the hand than I expected — the thinness really helps here. And the screen is just stunning; it looks more like you're touching pixels than ever before, and the rounded edges make it somewhat easier to hold. I have big hands and can reach across the the entire display with my thumb one-handed, though, so I'll have to ask someone with smaller hands here what they think. I'm especially curious about the double-tap on the home button that slides the interface down to make one-handed operation easier; I'll never use it since I don't have to, but it's a unique riff on the idea of one-handed operation.
(Update: I asked my friend Joanna Stern about the size and she flatly told me the 6 Plus is too big for her. So.)
The protruding camera is indeed a bit strange; I can't help but wish Apple would ease up on its relentless pursuit of thinness in favor of a slightly thicker phone with longer battery life, but like I said, the thinness is what makes the large size manageable.
And that large size is pretty key; this is the phone that's going to force Apple to turn the iPad into a true laptop competitor. I have an iPad mini that will never come out again once I get this phone; I have an iPad Air that will need a better reason to come out than simply the size of its screen.
As for using the thing, it really feels like what Dieter Bohn is calling an "iPad mini mini" — turn it into landscape and there are riffs on the iPad two-pane interface everywhere. There's also a new wider keyboard with extra keys including dedicated cut / copy / paste buttons and arrow keys, and new notes and emails open in a "sheet" over the main interface. It's unique, in the sense that Apple is very good at crafting distinct interfaces for distinct screen sizes; Android just gets bigger at larger sizes but iOS gets different.
It was somewhat hard to play with the camera in the demo setting, since Apple spent time and effort making sure the room was well lit and the new optical image stabilization system is designed to improve low-light shots, but it seems like a worthy update to the already-great camera in the iPhone 5S. Video features like the new 240fps slow-mo mode and the timelapse mode worked, insofar as taking slow-mo and timelapse videos of other people monkeying with phones is indicative of video features working.
Overall, though, the iPhone 6 Plus already feels like the iPhone I've wanted ever since I got an iPad mini. I think a lot of people will probably feel the same way.