The quality and pixel density of iPhone 4 screen is impressive, no question about that. However, 3.5" screen is too small by today's premier smartphone standards.
It is disappointing that Apple didn't kick up the screen to at least 3.7", to make it on par with Nexus One, Droid Incredible, etc. You can make the resolution 1920x1280 - but there is still only so much information you can usefully read on a small 3.5" screen.
4.3" screen with 480x800 resolution can display significantly more readable information than iPhone's higher res 3.5" screen. I'd take larger screen and less scrolling over high pixel density.
I'll take a phone that fits comfortably in my pocket. Going to 3.7" could work with a change in aspect ratio, but I don't want a wider phone just so I can have a monster display. I didn't initially want an iPhone because I thought it was too big, I don't know why I'd want a bigger phone.