3) The camera feels "better built" meaning it feels solid. it is not a typical point and shoot that you will be putting in a normal pocket though. It is quite bulky
4) There is a hot shoe and it is compatible Speedlites 270EX and higher. With a 430EX mounted it is very top heavy. However, you can use a ETTL cord for off-camera flash. They also offer a flash bracket to move the flash position to the left of the camera. It does not have full ETTL functionality.
5) The in-camera flash now pops up (from behind the Canon logo) and when it is retracted is off.
6) The ISO dial is gone from the top of the camera (it is now up arrow on the back) and the exposure compensation dial is now under the settings. The exposure compensation dial now goes -3 to 3 and you can immediately see the impact on the LCD.
ISO range is 100-12,100. Auto ISO is adjustable but the max auto is 1600 (I turn mine down to 800 usually). It is not very strong at higher ISO ratings. Of course, I am spoiled to the low light capabilities of the 5D Mark III now. But it is also not a professional level DSLR.
7) It shoots RAW (one of the reasons for getting a G-series in the first place) and you can shoot jpeg+RAW and change aspect ratios on the jpeg shots such as my favorite 1:1 "Photosquared" shots.
8) 14.3MP is nice and allows you to easily crop in on shots and still have good detail.
9) I do not do much video yet, but you can start filming with the push of a button from any mode on the camera instead of having to go to film mode. Built in stereo microphones (and wind filter function) but no way to hook in an external mic (that is a shame)
10) Max exposure time is 1 minute but there is still no "bulb" setting for night-time shooting.
Here is also a link to the full specifications on the G1X
The G1X fits a niche for DSLR owners looking for something smaller to carry with them as a day-to-day or travel camera. While it does not replace the flexibility of the DSLR with their inter-changable lenses and L-series glass, it is a great "back-up" camera and/or everyday camera.
Many of the shots that I share on Google+ and Facebook are taken with the G1X.
Here are a couple of my sample G1X shots: