After rolling with the new iPhone 4 for a day now, I am very impressed. Here are the most noteworthy new features, in the order I noticed them.
Oh, that glorious screen. Everything you've heard about how crisp the text looks is true. There's not much more to say—it's marvelous.
The iPhone 4 is fast, and I mean fast. This is especially noticeable for me, because I upgraded from the two-year old iPhone 3G. But it also outstrips Tracey's iPhone 3GS. This thing is the Firebolt of phones.
Two examples: Plants vs. Zombies, which I estimate at about a 40-second launch time on the 3G, is ready to roll in less than five seconds. And the process of syncing large quantities of data to the phone is also very zippy. I can't quantify this, but it seems that the bottleneck on that process was less about USB 2.0 and more about the iPhone 3G's ability to write to its hard drive. I was very surprised at how quickly the iPhone 4 was ready to roll after starting the restore from my backup yesterday.
The new camera is astounding. Not only does it benefit greatly from the speed boost on the phone, but the improved optics and the flash make it a legitimate camera for the first time. I don't own a point-and-shoot camera because when I bought my DSLR I never wanted to shoot with anything else, but having a serious camera on the iPhone will mean I can capture a lot of great images without having to plan to go shoot. I'm excited to see what I'll be able to do with this camera combined with my two favorite photography apps, Camera+ and CameraBag.
Fast App Switching
This is a function of the new version of the iPhone's operating system rather than the new hardware, but it definitely takes the entire experience up a few notches. The ability to leave a game to answer a text message and then return to it just as you left it almost makes up for the iPhone's lousy notification system. It's definitely a game-changing feature.
These are obviously just my first observations, tossed out in about 25 minutes. So far, I am absolutely pleased with the iPhone 4. It's unquestionably worth the upgrade price if you're on the 3G, and probably worthwhile for many or most 3GS users as well.