I picked up 12.3 over the weekend, and I'm afraid my limited use has been extremely disappointing. I've not been out on the highway as yet, but the street behavior leaves me very concerned:
The car will not do the speed limit anywhere. I've got my profile set to assertive and to go 10% over the speed limit, but I can't get the thing to do the speed limit in any location, even when I've used the accelerator to push it up to my normal desired speed. It wants to stay 1-3 mph below the posted speed on a clear day with a clearly lined road and no traffic.
Stop signs: the car stops the very millisecond it can recognize the stop sign 600-800 feet ahead. It brakes hard, then tries to recover at 15 mph or so. My biggest concern with 12.3 is getting rear ended: going from 50mph to 15mph in a hurry in a place nobody should be baking is a very big safety issue.
The lack of planning ahead is disappointing still. I have a well-marked but interesting intersection that most updates never seem to get quite right. I long for 11.3.4 which seemed to be incredibly good at predicting routes and lane changes, but everything since has been a crap shoot. With 12.3, the car chose the initial good lane, proceeded through the intersection, but then proceeded to move to the right lane - at a point where the right lane was about to end less than 200 feet up. It can clearly see there is no future there - even on the screen - but still wanted to change lanes (to go around nobody?) only to have to merge back again?
The car decided to drive down into a parking lane in a clearly marked roadway in advance of making a right turn 800 feet up. This is yet another new first.
Turns are indeed smoother. I'll give them that.
I could never drive with this with my wife in the car. She hates the thing as it is, but the braking behaviors for no apparent reason are a serious risk of accident. Some of the other decisions are quite concerning, but as much as I looked forward to this update, it's been quite surprisingly discomforting for my first couple of rides.
I'll still try it out on the highway. I'm in software, so I understand what testing is all about. I'll still give it a try in the city on my own, but this is a very disappointing release thus far, and one I can't really share with my wife in the car.