Intro
The iPhone6 is Apple's first foray into the arena of larger phones. It has a 4.7-inch (measured diagonally) screen, compared to the four-inch screen on the iPhone 5, 5C, and 5S, and the 3.5-inch screen on the iPhone 4 and 4S.
I am still using my iPhone5 for now, but I did get a chance to feel a 6 (not the Plus) when my mother's came in the mail today. In case anyone is unable to get to a store to examine the new phones, I thought I'd provide my best attempt at a detailed description. This is, of course,no substitute for playing with an iPhone6 in person, but it might help prospective buyers know what to expect, or answer some questions for those who just got their shiny new phones.
When I refer to any directions, I am always imagining the phone with its screen facing you, and the Home Button at the bottom (normal portrait orientation). If I say something is on the top right of the back face, for instance, that is the right as the phone is facing you, not the right if you were to turn the phone to look at the back face head on. This way, there is no ambiguity about where things are. When I say "edge", I mean the sides of the phone, not the edge of any face. For instance, the volume buttons are on the left edge.
Compared to Past iPhones
I'll first detail the differences you can expect between your current iPhone (any model) and the 6. If the 6 Plus is your choice, the following will still apply, except your phone will be larger and very slightly thicker than the one I examined.
First, the button on the top, used to lock or awaken your phone (I'll call it the Lock Button) has moved. For years it has been on the right side of the top edge, but now it is on the right edge, opposite the volume buttons. This makes it easier to press for many people.
The volume buttons and mute switch (that switch, if you haven't seen one, is just above the Volume Up button) are in the same place. However, they now feel different; on most iPhones, these buttons are rounded and stick out relatively far. On the iPhone6, they are elongated and stick out far less. The mute switch is the same size as in previous models, but it, too, does not seem to stick out quite as far. It is not so flush that you need a fingernail to move it, though.
Aside from those changes, all the other bits are in the same places - the charging port is centered on the bottom edge, the headphone jack is left of the charging port (if you have an iPhone older than a 5, that will be a surprise), and the Home Button is centered just below the screen. Aside from sticking out a bit, the camera is also the same, still in the corner near the Lock Button and with the flash just to its left. This will make OCR and object recognition apps easy to use, as there is no need to adjust to a new camera position.
For Everyone
Now that we all have a basic understanding of the layout, I will attempt to describe how the phone feels overall. Again, this is the iPhone6, not its bigger brother, the 6 Plus.
Rounding It Off
First of all, you should understand how the edges feel. Ever since the iPhone4, Apple has kept the edges of its phones squared off, unlike the slanted and curved edges of its iPods and iPads, or the rounded edges of the old 3GS. With the iPhone6 series, it has adopted the curved edge design, but not quite in the way you might be thinking. Where, say, an iPod Touch 4 has its back face slowly slant up to sharply curving edges, the iPhone6 has a completely flat back and front. The edges are the only curves; the aluminum back curves around to meet the glass of the screen, which itself curves down to meet the aluminum. It is hard to describe in words, but the edges are curved a bit like the spine of many American checkbooks. The phone is thinner than that, of course, but the way the spine feels is like the edges of the iPhone6.
The iPhone6 feels, at least to my hands, incredibly comfortable. It is a jolt at first if you are used to the squared-off edges of older models, but you quickly get used to it. Obviously, comfit and feel are highly subjective, but at least to me, the 6 is far more comfortable and easy to hold than my 5. The same holds true for phone calls - it is easy to keep the phone in place, and I never felt like I was about to drop it. Despite being thinner than the 5 or 5S, the rounded edges make it feel more substantial than it really is, lending the iPhone6 a slim profile that manages to feel thick enough to hold even though it is thinner than any phone Apple has ever made.
Display
The screen is the same as usual, but it extends a bit further toward the sides of the phone's body. Normally this won't matter, but if you use the phone in landscape mode, you will find that things are closer to the edges than you might expect. For example, a keyboard in landscape orientation felt like the bottom-most row of keys was about to slip off the display entirely, given how they rest at the point where the glass curves. This should not impact your efficiency once you get used to it, but it is something to keep in mind, especially for those who explore by moving a finger around more than they flick left or right - don't neglect to explore the edges.
According to my (fully sighted) mother, the display on the 6 looks sharper and somehow… better. She was unable to put it into words, but looking at photos, text, and anything else on the screen is more enjoyable than on the 5. I mention this because low vision users may find it interesting; aside from the larger display, it also looks better. Low vision, of course, covers a massive range of conditions and visual acuities. Yet again, I encourage you to experience the 6 for yourself to see if it will make a difference for you.
Protruding Lens
The camera lens, as I said, sticks out a bit. If you use your phone while it is flat on a table or desk a lot you will want a case so that there is no wobble, probably. I say probably because, despite the protruding lens, there is really not much wobble to the phone during normal use. It is noticeable, but it doesn't seem to impact gestures or cause the device to move around. Still, just as with all iPhones, a case might be a good idea to protect the lens; yes, it is coated in sapphire, but my motto is "better safe than sorry".
Buttons
To me, the buttons on the 6 feel a bit clicky. All iPhone buttons click, as well they should, but the ones on this device seem to be very slightly louder. The feel is the same, so if you have motor problems but can manage the buttons on your current phone, you should be fine with those on the 6. The smaller volume buttons and mute switch may give some difficulty to some users, but that is yet another reason to seek out an iPhone6 to handle before you decide if you should buy one.
Final Thoughts
Overall, the iPhone6 is an extremely comfortable device to hold. I tend to hold my phones in my left hand and execute gestures with my right, rather than using one hand for everything, and the screen real estate on the 6 makes this a joy. The phone also feels solid, secure, and light in my grip. I know it's there and I don't feel like I might accidentally drop it, yet it is light enough to not be a burden at all. The iPhone5 and 5S are a similar weight, at least to me, but given the increased size of this new device, the continued lightness is an impressive feat. If you are upgrading from a 4 or 4S, you will definitely notice, and appreciate, the drop in weight. The iPhone6 is the thinnest iPhone yet, but somehow the curved edges and overall feel and balance combine to make it feel thick and substantial enough to hold an use comfortably.
If you are thinking of upgrading but are concerned about the size, I would say this: don't be. The 6 Plus may well prove too large for many people, but the 6 is, from my perspective, really not much larger than the 5 or 5S when held in the hand - you'll know it is bigger,of course, but it won't be the huge change that going to the Pus might be. Please, before you make your final decision, try to get some hands-on time with the iPhone6 and 6 Plus to see exactly how they feel. However, I would urge you not to dismiss them out of hand simply because they are larger and you don't think you will like or use the bigger screen. I find VoiceOver gestures easier, having more content on the screen is nice, and there are other advantages. You can read my take on the iPhone6 in my recap of Apple's September 9, 2014 announcements.
If you have questions about the iPhone6, or if I left things out and/or was not clear, please leave a comment. It is very difficult to explain the physical aspects and feeling of a device using only words, and I know I probably didn't do the iPhone6 justice. It is a really nice phone to hold and use, and I found myself preferring the feel of it over my iPhone5 within ten minutes of use. I'll end by saying this: if you give the iPhone6 a chance, you might be amazed at how much you start to really like it. Of course, you might not be, but you'll never know unless you give it a try.