I've owned this handset since Dec 23rd (or so.) Aside from a inconsistent issue w/ WiFI dropping, the phone has been awesome. Currently the phones runs Android 7.0 (Nougat) and is smooth and silky, with next to no lag or hangs. I'd say this is the best phone I've had. I have owned (in reverse order) a Moto Droid Turbo 2, LG G3, Samsung Galaxy S5, S4, and several other handsets from all major builders (with the exceptions of Apple and Sony) including HTC and Blackberry/RIM. This is, by far, the best phone I have owned.
Design wise, I am enjoying this phone. I am familiar with the ShatterSheild LCD Motorola/Lenovo have employed in this phone, as the Turbo 2 I owned prior has this as well. That phone lived through quite a few face-first impacts on gravel and concrete with only minor scratches to the plastic LCD surface. Knowing this, I did put a glass protector on the front of the Z Force.
The overall design of the phone feels a bit awkward without the included Style Mod being on the back of the phone, as the aluminum case has some sharper edges where the mod is supposed to blend in. Given that leaving a mod or case off of the phone would expose the module contacts on the rear to the environment and possible damage, I'm not sure you would really want to use the phone without anything covering the rear.
The hardware modularity is an awesome idea, and I like how it is implemented. Currently, I have the Tumi Wireless battery mod, which gives me around an extra day worth of charge, and allows me to use my wireless pucks from my Turbo 2. This has proven invaluable on occasion, as I often find myself at work with no USB-C charger and a dying battery on account of the long battery life and my ADHD. I look forward to more mods coming out in the future. My one complaint in this area, is that while the battery mod is on the phone Bluetooth and WiFi ranges are notably decreased. On more than one occasion I have picked up my phone with the mod on it and the sound coming from the linked BT device has dropped or gone "robotic" as the signal fades out. Given that the antennas are on the aluminum rear panel of the phone, this is understandable.
WiFi on this phone seems to be pretty strong, although it occasionally will drop and fail to connect (this requires a reboot to fix, which isn't a big deal to me.) Having the WiFi power save seems to prevent this issue from occurring, although I have not really done much experimenting to confirm this. The issue doesn't present itself often enough to determine a patte, and as a result it isn't really a bother to me.
Overall call quality is decent compared to my other handsets, and people on the other end haven't complained about call quality. HD Calling seems to be a little weaker than my Turbo 2, as areas with poor service drop sooner than they did before. Again, not really a bad issue since I spend most of my time in stronger areas or on WiFi, where the calls can be routed over WiFi if the cell service is weak.
On the whole, this is an excellent phone that excels in durability and usability.