Just received and tested FSD 12.3. It is definitely different and looks better.
Some specifif observations:
[+] Auto MAX speed selector is a big positive factor, especially at lower speeds. So, for instance, I have 25mph speed limit in the neighbourhood. Before that, Tesla would just use my setting (=25mph), without slowing down for parked cars, etc. In my case, it now drives around 20mph, which is more convenient.
[+] It accelerates fast when neeeded, but not too fast, which is more convenient than it was on FSD 11.
[-] It can still mislabel red traffic light for green (!). Not as bad as it sounds, though. The car stopped at RED. Then it decided it turned GREEN (it wasn’t!) and started driving, but it quickly realised it is still red and quickly stopped.
[+] Lane changes feel more natural.
So it still can fail at pretty basic stuff, but at least right now I’m more confident in letting FSD drive in minimal or moderate traffic (or traffic jam).