My first thoughts:
- Happy about the removable battery and microSD slot. I wouldn't want to miss either. The slightly smaller battery is not necessarily an issue as long as the Snapdragon 820 delivers on significantly improved efficiency over the 810. Also, the display is a bit smaller and thus less of a battery hog.
- Not keen to see the volume rocker moved to the side, but I agree with Phil that the power button / fingerprint sensor is the more important part, and it is still where it belongs: on the back of the phone.
- The dual camera setup is interesting, but we will have to see about the image quality of both.
- I like the modular concept overall. It potentially offers more (and better) customization options. Some of these add-ons will likely turn out useful, and others not.
- I find it interesting that LG continues to use IPS technology for their displays, despite all the resources they have poured into OLED technology over the last few years, including flexible displays and a massive OLED factory they just opened in Korea.
- I'm not keen on the all-metal finish - I prefer the leather backs of the G4. On the upside, the metal frame is going to make the device sturdier.