The speakers seem noticeably better--or at least, louder--than they were on the 4S and 4. Part of that may be the changes in phone's volume and shape, which could provide more open air in the case. They're still no match for a good pair of headphones, but you can probably get away with watching a YouTube video without everybody around you saying, "What? What did he say?"

The Home button is distinctly stiffer than in iPhones past. It has a sturdier feel and seems to require a firmer touch than Home buttons of yore.

The improved front-facing camera--now in HD quality--is quite welcome, particularly for FaceTime calls.

Overall, while it feels like a very significant and substantial upgrade, it also still feels like the same old iPhone. For many of us, that's a good thing.