Used an iPhone 5 yesterday for a few minutes. Decent build quality, very light, very thin. Amazing screen clarity and vividness - unequaled.

Here are my issues:

Too light. Feels cheap compared to iPhone 4 or original iPhone.

Too thin. Not anywhere near as comfortable in the hand as an iPhone 4.

Too narrow. Going tall with the screen doesn't solve any problems, it only adds a check-mark for 4" screen to their spec list.

The screen (STILL!) has a visible black border around it - this is jarring on the white iPhone and really should have been hidden.

It would have been so much nicer had they gone for an all-stainless steel design instead of using aluminum. I don't use a case or bumper on my iPhone 4 and in 2 years of use, it's still spotless. The iPhone 5 is not going to have that kind of blemish-free longevity.

I also used a Sony Experia briefly and its screen is just about the size I wish Apple had moved to - both wider and taller, but still very comfortable in one hand with using only a thumb to navigate. At a visual inspection is seemed about 5mm wider, the exact size I'd advocated Apple moving to. But of course the screen quality doesn't hold a candle to the iPhone in terms of clarity, density and closeness of the pixels to the top glass surface. But it felt like a great phone and miles ahead of the Samsungs I've used in fit/finish.

Apple will do well with the iPhone 5 and I'm confident they'll outpace their iPhone 4 sales. But I think they really missed the boat not moving to a larger screen in this generation. It only causes the potential for additional friction and fragmentation should they choose to do this later. And if history is any indication, there won't be any format changes next year with the expected iPhone 5GS.

Overall impression after having lived with an iPhone 4 for 2 years. Not impressed.