Well it's NOT going to be like Samsung's. The code of the HomePod firmware indicates that it works with Infrared, which would be much more faster and more convienent than the Samsung approach.
Why does everyone think it'll be terrible?

Do you guys really think Apple would add this half-hearted approach?
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Here is how it'll probably work:
-Your phone is in a locked state. Face ID is turned off.
-You activate your phone either in a laying state or in your hand (raise to wake, tap on the screen etc)
-Face ID is active and recognizes your Face -> your phone is unlocked but stays on the Lock / notification screen
-Awareness detection kicks in
-You look away or someone else takes your phone (your phone is still on the lock / notification screen)
-The awareness detection detects a face other than yours -> the phone locks.
Of course if you are passed the lock / notification screen your phone will still be accessible. But that is the same with Touch ID.
I think Face ID will be huge. It will work seemlessly, and add another layer of security to it.