So I've had the Reverb G2 for a week now and have some thoughts.
The overall size, feel and visuals are very similar to the original Reverb.
I think the FOV is almost the same. IPD adjustment is nice to have. The sweet spot is somewhat larger at least partially thanks to this fine-tuning. LCD color saturation and contrast ratio looks the same to me as the original Reverb. Lens behavior with respect to distortions and god rays seems similar in too in that there are the usual small issues but not as annoying as the Odyssey+ can be. However, the Odyssey+ has such better color and contrast ratio that I sometimes use it instead for dark games.
The 2 side cameras definitely have tracking benefits. I think they have plenty of the sides covered now unless you need to reach behind yourself for some reason lol. A camera facing up might be a nice addition yet but the sides were the biggest issue before. Tracking still isn't perfect with the holding-still scenario for say gun aiming or whatever. Room setup still needs some planning of course. It needs to be fairly well lit, there need to be detailed surfaces, no reflections, no sunlight, etc. No real complaints here besides the usual desire for that elusive perfection lol.
The original Reverb is the most comfortable out of the 3 HMDs I have. It's lightweight, keeps light out, and fits my face nicely. G2 has a magnetically-attached plastic facial interface with pad. This makes it super easy to remove for cleaning. However, the fit is worse than the original Reverb in that it is too narrow and presses on my temples and upper cheeks, which is a catalyst for pain and nausea. Ooops. Small-headed folks at HP I guess. I've seem the complaints of other owners and read that VRCover's replacement interface + masks kit works great so I ordered one and it is indeed the answer to that problem.
The controllers are the most unfortunate aspect. They created their very own WMR control scheme by removing the trackpad and adding two buttons instead. They also changed thumbstick click from being the SteamVR menu button to the right controller menu button which, you guess it, some games were using before. These two aspects have broken compatibility with so many games. Many games have received updates, and the SteamVR UI sometimes has user-shared game-specific control schemes that work. You will run into some games that you must fix yourself though and that's hit or miss. I read I can pair any WMR controllers with it but I haven't bothered to do that yet.
The mini ear speakers which are similar to what the Index uses are interesting. People seem to be crazy about them. There is added immersion with the lack of contact with your head and the sound is very airy, open, and has good positioning which gives the impression of hearing sounds from the room you're in. However they don't sound anywhere near as nice as even a $10 set of earbuds, with particularly poor low frequency response and that is a loss to immersion. Unfortunately the headset lacks the original Reverb's convenient headphone jack.
With respect to USB compatibility, it seems much improved over the original Reverb. The original Reverb and various other USB-powered HMDs had problems with internal HMD USB devices resetting, probably due to a combination of USB voltage drop and signal integrity issues from the long cable in combination with poor motherboard USB routing. The G2 has a small external power brick that attaches to a small box that the other cables join into before becoming a single cable to the HMD. It seems likely that this has some USB signal repeating hardware inside. The end result is the G2 has 6 meter cables (2 meters longer than Reverb) and I haven't seen any strange behavior from it.
Another interesting thing I noted is the cable is made from a material with a tacky/grippy surface. I think the idea here is this helps prevent it from sliding around on your back and ending up in front of you as you move. Unfortunately it is also somewhat irritating in that it grips your shirt and wants to move with you. It's weird. I'm not sure if I like it or dislike it heh.
The cable is easily detached from the headset. You pop off the magnetic face interface and this gives access to the cable port. The connector is somewhat like a Displayport connection and seems very solid once it engages. This feature is nice in case you damage the cable, but I've read it's very difficult to get a replacement so it seems to be a moot point.
By the way, I've discovered owning multiple WMR headsets works quite well because they all identify with the same room calibration. Plug in and go with no special setup for each. I thought maybe the 4 camera G2 might be troublesome in this respect but nope it works fine and locks in the room just like the others.
What I want next is something with OLED style contrast ratio but with Reverb clarity. I find myself accepting the somewhat soft image of the Odyssey+ just to be able to enjoy the lack of grey fog.