Honestly, the iPhone 4 was a let down for me today.
The 3G to 3GS felt like a bigger upgrade to me, and I know that makes no sense as they looked identical.
The iPhone 4 looks cool, but it feels very odd in your hand. The signal issues are annoying at best.
Plus, there isn't much more you can do with it than a 3GS. I will probably never get to play with face time, much less use it for something worthwhile.
The 720p video recording is a high point, but how much mobile video do I need to take? Not much.
Overall, it's obviously still the best phone out there, but I think the 3GS was pretty great honestly.
I buy everything Apple and always construe things to make them sound better. THis is probably my only let down *EVER* with an Apple product.
Again, not saying it's a disaster, just a let down, and I am normally blown away.