Only slightly bigger than Sony's RX100 series, the ZS100 at least has a slight grip.
As is common among enthusiast compacts, the ZS100 has a ring on the lens that you can program for specific functions, such as adjusting aperture or shutter speed.
You'll find the typical Panasonic touchscreen interface on the ZS100.
It's a bit smaller than the one on the later RX100 models, but it doesn't require you to pop it up, which makes it slightly more enjoyable to use.
You charge the battery via USB.
The new Post Focus capability -- choosing one out of a burst that has the focus area you want -- is a mode you shoot in that's enabled by pressing that Fn2 button.
The 4K shooting modes are accessible via the Fn1 button instead of on the mode dial, where they've been on other Panasonic compacts.
It's not terribly deep, but given many manufacturers' aversion to putting grips on compacts these days, I'm surprised it's got one at all.
The lack of a hot shoe may dissuade some buyers who might consider it instead of the LX100.
Though the lens's maximum aperture rises to f5.9 as you go through the zoom range, given that it extends out to 250mm equivalent that's not bad. What matters is how quickly you get there.
As mentioned previously, you can tilt the flash while shooting to bounce the light.