In order of importance:
- Dual cameras in a smaller physical device
- The best display ever shipped by Apple
- More physical display area than similarly sized iPhone 8
- Two hour longer battery life than similarly sized iPhone 8
- 1GB RAM more than similarly sized iPhone 8 (3GB vs. 2GB)
- Better telephoto camera (brighter, stabilized) than the 8 Plus
- Face ID and related AR enhancements - can use with gloves and in the rain
- Polished stainless steel band design reminds me of my original iPhone
- Front camera supports portrait mode
- Improved cameras (larger sensor, deeper pixel wells, etc)
- Wireless charging
- Fast as hell CPU/GPU
- Louder speakers (I particularly hope the top speaker is louder than my 7, which is drowned out by the bottom speaker and throws off the stereo effect somewhat)