@luke55 The sleep tracking least for me has improved substantially since its introduction and there will be ongoing improvements. The sleep tracking shows sleep phases, which I tend to have difficulty believing anyway as those are difficult to detect without professional equipment so I think not so basic. As you can see on the forums sleep tracking works very well for some, less for others.
As I stated before you should wait until the watch notifies you of your sleep results, this is to prevent it from thinking you did not go back to sleep when you got out of bed in the middle of the night. You could turn off DND or do some other action before taking the watch off and the sleep notification will trigger.