It will have a TALLER screen. Width will remain its narrow format. The hardware is below what the current crop of Android phones are (with the exception of the screen) and IOS has no standout features above what IOS 5 has. As I tell people, it is a simple phone for simple people.
"Simple" folks vastly outnumber us geeks who dwell in the forums
The iPhone 5 will sell a lot more devices than the GS3 or HD, with VZW.
Total phones should still be the GS3, but that is worldwide. Should.
I can understand simple and performance. Case in point, Games like NOVA 1, 2, 3, MC3 and others play smoother on my iPod 4 and iPad 3 than they do on my GS3. No comparison. Regardless of why, they simply just do. My guess is partly due to the coding effort with the Android versions is not the same as the iOS versions. That and the multitask environment if Android (a lot more stuff battling for memory channel bandwidth).
Added:
Still, I prefer my GS3 over and iPhone 5

A little harder to choose though with the tablets. Were it not for the great game emulators, I would probably prefer the iPad 3. Probably.
As far as legacy games on the iPhone 5, they will either have black borders on the sides, or be squished looking to fit the display. This will be a dilemma for programmers with all the legacy device owners, since they will need to code for both- If the option for legacy devices is to have proper ratio, this would probably mean black bars on top and bottom and smaller viewed app as a result. I do not see how this will end happily for all legacy device owners.