Temperature is only recorded during activities, and as it's measured inside the watch the value is somewhere between body and environment temperature. Unless environment and fit of the watch are controlled, I would not expect useful readings.
The oxymeter is also not very good, probably because the position at the wrist is suboptimal and the sensor isn't opposite of the LED. The light shines into the skin, not through it, as with the oxymeters that are clipped onto a finger. Measurements take about 20 seconds and are wildly off and inconsistent. I just measured 99-100% saturation with a clip-on oxymeter and 92% with my watch.
The value I trust most is the resting heart rate. It's not just the minimum value recorded, the watch seems to apply some heuristics to figure out whether a measurement was clean or not. The sensor data itself must be very noisy. When the "abnormal HR" feature is turned on, I get false alarms multiple times per day. I had a colleague who thought her HR was pretty constantly at 60, because that was the default value of the Fitbit that she wore like a loose bracelet.
To provide some anecdotal data, I had a bronchitis last year and the RHR went from 49 to 69 at its peak. At the same time, the "Body Battery", which is calculated from HR data, also went down to 0%. I was surprised that the feature actually works, but definitely didn't need it to figure out I am sick.