I had a 3G with a broken screen, actually 2 3G's with broken screens.
To 16 GB iPhone 4 [ black ] :
iPhone 4 is absolutely amazing. Screen is out of this world. Camera is magical [ video, tap to focus, flash, 5 Mega px, focus] . Video calling feels like the jetsons. The product design and materials are Grade A. BAttery last way better than the old phone. iOS4 is a decent improvement from 3.2 . although the hardware upgrades are much more noticeable for me.
The Bad News:
Yes reception is iffy, probably worse than before. But by like 1O%- 15% . So in the big picture its not that big of a deal. I suspect we will see some software updates from apple trying to fix these issues. You got to give them at least a month to collect some data, come up with solutions and bring them to market.