Okay, so, I stopped by the Sprint store today and gave the E4GT a good workout. I'll give some thoughts here, and note that although I currently have a Photon I have no vested interest in it over the E4GT. Indeed, I'll be deciding soon between the two, because my wife needs a new smartphone and will likely get a Photon whether it's mine (and I get the E4GT) or her own.
1. Build: The phone is very light, almost too light, and it's noticeably bigger than the Photon. Personally, I like the Photon in hand much better than the E4GT--the Photon just feels more solid to me. The E4GT's build quality is probably very good but the lightness made it feel a little cheap to me. Winner: Photon.
2. Screen: The E4GT's screen didn't seem noticeably better to me than the Photon's, and note that I'm one who doesn't notice the "screendoor" effect. To me, the colors on the E4GT were blown out as usual, it wasn't as bright, and I didn't like the resolution. Comparing the E4GT to the Photon side-by-side, I felt like the E4GT was something intended for a preschooler. Text was crisper on the Photon, and the screen was brighter on auto. Winner: Photon.
3. Touchscreen: I was very disappointed to find that the E4GT was displaying the same missed touches on the capacitive buttons as my Epic did. On a number of occasions, I had to hit the home and back buttons more than once to get them to register, which reminded me of one of my frustrations with the Epic. Overall, touch seemed less responsive than the Photon, which is perfect in this regard. Winner: Photon
4. Performance: I noticed some lag when switching home screens on the E4GT, pretty much identical to the sorts of lag I experience with the Photon. Nothing major, but there. Opening and running apps seemed pretty much identical. I also MUCH prefer the screen transitions on the Photon, including moving from landscape to portrait and back. Not only do I like the smoothness of the transition effect on the Photon, but it's quicker. The E4GT hesitated sometimes in changing orientation, which always bugged me on the Epic. Winner: Overall performance a tie, transitions Photon.
5. Skin: TouchWiz 4.0, which I love on my wife's Galaxy Tab 10.1, doesn't translate as well to the phone. It seemed much more cartoonish to me on the E4GT, with overly bright colors in some places and then the unpleasant dark color scheme with the calendar and such. Although the widgets seem nicer on the E4GT than the low-res widgets in the Photon's skin (proto-Blur or whatever it's called), overall I like what Motorola's done here. Winner: Photon.
6. Screen: Did I mention that the screen is really big and the resolution means everything just looks unnecessarily large? Oh, yeah, I did, but it needs to be stressed: if you're gonna give us a 4.52" screen, then give us a resolution to go with it. Otherwise everything's just blown up to no purpose.
Overall, I think that if my wife ends up needing a new phone right now, she'll likely get her own Photon and I'll keep mine. I can see no good reason to get the E4GT over the Photon, and a number of really good reasons to pick the Photon over the E4GT. I doubt we'll see a difference in real-world performance, I prefer the brightness and crispness of the Photon's screen, and the Photon just seems like the more elegant, serious, and powerful device because of the more solid build, extra heft, and screen transitions.
My personal opinion is that the E4GT might be the better-spec'ed device in some ways, and benchmarks better, but the Photon is the better smartphone overall. And that's not even to mention the likely superior Motorola radios, which I didn't get a chance to compare. But that's one of the things that's impressed me most about the Photon--I honestly don't think a smartphone can perform _better_ than the Photon as a phone.