Overall, the iPhone 6 is a very nice evolution of the iPhone 5s with a bigger screen. It outperforms the iPhone 5s in almost every single way. Here are some things I noticed in my first few days of use.

• Compared to the iPhone 5s, the iPhone 6 is big. This really changes how it can be used. I’ve found the iPhone 6 harder to use one-handed while lying down. I can’t imagine using an iPhone 6 Plus one-handed at all.
• The larger screen has made two-handed typing better/easier, but again, one-handed typing suffers here. The swipe keyboards in iOS 8 help, but suffer from other usability issues due to API limitations. The key one for me being 3rd party keyboards not having access to the native keyboard picker/switcher. The native switcher allows you to drag up from the key to pick a specific keyboard, whereas the 3rd party keyboards can only switch to the next keyboard. I hope this changes with future SDK changes.
• The rounded shape is really nice and comfortable to hold. The rounded glass on the front lends itself well to the edge-based gestures in iOS ⁷⁄₈ (such as when navigating back by dragging from the left edge of the screen). The shape is very original iPhone-esque. I love it.
• The screen is gorgeous. It may be partially due to the rounded glass, but the screen also feels closer to the surface than before, making interaction feel even more direct. The screen seems cooler in color temperature compared to the iPhone 5s, with a yellow tint on the iPhone 5s relative to the iPhone 6 when viewed side by side.
• The protruding camera is an aberration on an otherwise very sleek device. It does provide near-bulletproof focusing (using phase detection autofocus), and the video features (240fps slo-mo and stabilization) are nice. There’s also less noise under low light conditions compared to the iPhone 5s. It’s getting harder to justify carrying around even my Fujifilm X100 when on-the-go/traveling.
• To get rid of the protruding camera, I opted for Apple’s leather case. I liked the one I had for the iPhone 5s, and the case for the iPhone 6 is very similar. I’m glad Apple made all the colors darker to avoid the “dirty” look the iPhone 5s leather cases would get after a couple months of use. The more open bottom also means my fatter headphone plugs can fit without an extra adapter. The only con is the raised lip around the screen breaks the flow of the rounded glass, and can make some edge-based interactions more difficult. The most obvious one to me is when trying to move apps between screens.
• Speaker seems louder and slightly better, which is nice for podcast listening while doing chores. The vibrate motor also seems stronger to me.
• Too many apps aren’t ready for the big screens, and run in a zoomed mode. The biggest problem here is how the keyboard becomes taller, and is noticabely jarring when switching between scaled and non-scaled apps. I can’t imagine how much more ridiculous this must be on an iPhone 6 Plus. This is almost as bad as a pre-iOS 6 app not getting updated. It looks like some of my main daily driver apps are getting updates out very soon, so this may improve very quickly.
• With a bigger screen, it’s even more crucial to have edge-based gestures available for app navigation. Reaching up to the corners is a chore. Reachability (tapping, not pressing, the home button twice) helps, but swinging the thumb down isn’t always easy depending on how the phone is held. It feels like some apps do need to adapt their UI to be more big-screen friendly, as reaching for the top corner is less viable now.