Ok, a comparison to other phones is not that reassuring, because many phones on the market are flimsy. Compare it to the iPhone 5. That thing was built like a tank compared to the competition.
I traded my iPhone 5 in, because I got $200 for it. But I fear that the 5 will turn out to be the pinnacle of iPhone achievement. I wish I could have bought a new phone with the iPhone 5 case design but with useful tweaks like NFC and an improved camera.
The iPhone 4/s was even more solid, and I think very attractive. A stainless steel frame has its advantages (especially since I think weight is a non-issue with devices this small).
More solid but over 20% heavier than the 5. An iPhone4 weighs more than the much larger iPhone6. I think they're all under the maximum weight threshold for how much a device like this should weigh, but every time I pick up my wife's iPhone 4 it subjectively feels heavier than my iPad mini, even though it's less than 1/2 the weight.