In the hand the iPhone 6 is light, on the scales it's heavier than the 5, but in the hand it feels about the same weight - spreading the mass over a wider area no doubt creating this illusion. The Space Gray version that I tried looked like a cross between an iPad Mini and a MacBook Air. In the hand it doesn't feel large at all - although you should remember that my daily driver is the Xperia Z1, which is far larger.
I didn't like the way that the camera protrudes from the back of the new iPhone, it's a messy detail and I would have much preferred the iPhone to stay the same thickness as the 5S and retain a flat back. This obsession with making the iPhone thin is counter-productive and I'm sure that no-one will actually be able to tell that the new iPhone is half a millimetre thinner than the old.
Otherwise the casing is nice and tactile, the rounded edges and curved screen change the user experience over the chamfered, square sided 5 style. Which is better though? The iPhone 4/5 design was ground-breaking and the 5 in particular sports probably the ultimate expression of that design ethic. Nothing looks like an iPhone 5 unless it's trying too hard to look like an iPhone 5.
The iPhone 6 design is much more anonymous - I didn't find it stood out at all - in fact I walked past one on the display in the shop two or three times before noticing it amongst the other phones there. Given that most people will be wrapping it up in a case that's probably not a big issue. What it does emphasise is what a good job HTC have done with the One M8 which looks and feels far more of a premium phone.
And so to the raison d'être of the iPhone 6 - that 4.7" screen. I have to say I was left a little underwhelmed by the new display. Yes, it's as bright and sharp and reproduces colours as well as the iPhone 5's, but it's not a step forward. Alongside the HTC's display it gives up both size and resolution, without outperforming it in other areas. The HTC's display is noticeably crisper. Against the S5's display the iPhone is lacklustre. Now I know that many people don't like AMOLED's 'artificial' colours, but given that the Samsung manages to deliver true black and a highly customisable temperature/white point I don't believe that remains a valid criticism. If this was just a choice between displays the S5 would be a clear winner here.
Given the bigger display Apple have created a one-handed mode called 'Reachability'. This is a complete kludge and I don't believe it's even necessary on a 4.7" display, but if you're going to do it, do it properly. Double tapping (not pressing) the home button removes the bottom half of the UI and replaces it with the top. I'm not impressed. Samsung have executed this is a far better way. Slide your thumb in from the side of the S5's display and back out again and the whole UI shrinks to around 75% of it's original size, allowing true one-handed mode.
Otherwise this is an iPhone - just bigger. Unlike the bigger iPhone 6 Plus there are no two panel landscape displays to make use of the extra screen real estate, nor will the home screen rotate. All of the other improvements in iOS 8 are present here but little extra over what's in the 5S.
Ultimately it's an iPhone with a bigger screen. Current iPhone owners will lap it up. iPhone owners who switched to Android solely for a bigger screen may well switch back. However I can't see a massive swing from Android to iPhone as a result of the iPhone 6 though. It's just not that much different than what has been before.