Only one full day with my SIM in it and I like it alot! But it's definitely a bit of a transition from my Nexus 6. I feel like the display and typing are a bit cramped and yet still not quite narrow enough to be comfortable holding and typing in one hand. Otherwise it's a powerhouse. Everything is snappy. The battery seems great. I was on track for 9 hours SOT with no SIM, only WiFi. I had over 4 hours SOT on full day one, but that was hard use with lots of tethering for my Nexus 6 to backup stuff from there and then downloading to G6 and installing apps and such. I think more like at least 5 hours SOT will be my experience with normal usage.
Display is fantastic, though my eyes aren't what they used to be and I think I would be just as happy with 1080p for an LCD this size (I feel OLED are not as crisp and definitely benefit from higher resolution, but probably not necessary here). Auto brightness is perfect for me and colors and blacks are great even coming from an OLED device. Not sure why others are having trouble with screen brightness, maybe they have screen protector that interferes with ambient sensor. The low brightness in dark room and brightest outside are great and normal indoor use adjusts perfectly for me, so much nicer than Nexus 6 auto brightness, which doesn't handle the extremes well.
I definitely miss a few things from the Nexus experience (settings layout, Google dialer, no bloat, updates), but the G6 US unlocked version has very little bloatware and overall is a pretty great experience.
At first I was a little annoyed with lack of side power button, but tap to wake and sleep is the best thing ever! I am already tapping on my other devices expecting them to wake.
My main reason for upgrading was the camera experience on Nexus 6 which can take great HDR+ photos, but the camera is so painfully slow to take the shot and even slower to process it. Normally can't take a second HDR+ shot for 30 seconds. My daughter is used to holding a pose for 5 seconds while it captures the shots. G6 is a great camera. Though I will normally use auto, I love having the manual controls. I also love the slightly narrower than average main lens with supplemental wide angle. G6 has only slightly more detail than Nexus 6 HDR+, but better dynamic range and low light performance. Unfortunately I think the front camera is a little weak for a flagship especially in low light.
Speaker is plenty loud, but a little tinny or echo or something and I definitely miss front facing speakers.
And I really didn't want to give up wireless charging, so I am extremely happy it has that!
I expect I will probably still get a larger Pixel XL 2 or small tablet later in the year, but I really have no complaint about the G6. I know most people don't feel the same, but if it was a half inch wider I think it would be nearly perfect for me.