Got this on pre-order and so far happy with it even 2ith some of the shortfalls.
I upgraded from the GWA2 44mm and as after previously having a WearOS watch I knew battery life was not that good on a non LTE model, so quite surprised to see that after 1day 13hours it still had 23% battery and reported had 11 hours usage left.
The things that currently don't work is Blood Oxygen during sleep even though it is enabled, but works if manually perform the test.
Google Assistant, Google Pay and YouTube Music are not available, even though the first two are supposed to be on the device
The device is not listed in WearOS and must use Samsung Wearable app, older WearOS faces still require Google Fit (not installed) to work so will need the Health Sync app to sync data to Google Fit.
Samsung Watch developers are starting to release WearOS faces on the Play Store, so hopefully existing WearOS developers start creating their designs to work with it.
In regards to installation of watch faces, most now have to be installed by the web Play Store or on the watch itself as trying via the PS results in device not compatible.
Hopefully with the pending update that is reported to be released it may fix some of the issues with Google apps missing and bits not working.
As for the shortfalls, I'm guessing that's something that Team Sammy can fix. I share the same experience with the Sleep Oxygen Tracking, and I've also shared a post about it, so hopefully that'll make a bit more noise for the team.
Hopefully as the watches become more mainstream we'll get more improvements and fixes from both Team Goog and Team Sammy.