These are just my impressions.
I handled my friend's iPhone 5 today. Not very impressed. The lightweight-ness did throw me off, and the device does feel a little cheapened, but I oddly can't put my finger on exactly why. It feels as if it's been hollowed out; almost as if I pressed it, it would give in and be crushed, or at least flex. It's also lost some of its former grace, especially with the back. The back looks more utilitarian and rugged, which can be a good thing actually. It's just a stark contrast from the 4S' full glass black. I was never a big fan of it, but there was no denying the glass made the device seem more graceful and elegant.
To me, the iPh5 is just awkward as heck. It really feels significantly taller, even though I know it's not. The lack of expansion width wise feels bizarre, like it's more a chocolate bar than a smartphone. I'm sure if I ever owned it and spent days with it, I'd adjust, no doubt. I do love how thin the device has become.
I also disliked that the power/sleep button is now even further away to reach at the top. I loathe the power/sleep button on the HTC One X. It made it horribly clunky to put to sleep (and wake in the HTC's case). It's a very close clunkiness with the 5. You had to adjust your hand so that your index finger could reach it. For those who argue the importance of the ease of use with one hand, that power button sure complicates things.
There's no describing how comfortable and perfect the location of the power/sleep button is on the GN. If 'm holding it with my right hand, my thumb is always nearby. If left hand, my index is always wrapped nearby. The power button on top needs to go the way of the dinosaurs. It's making less and less sense. The front home button definitely felt helluvalot more sturdy and durable though. And the screen is pretty vibrant and gorgeous to look at. No arguing that. In my opinion though, it's still not big enough. Reading texts and websites were really no different than the 4S. Certainly better, but not enough.
And iOS is simply what it is. iOS.
Just my impressions.