Is the caster required to see the target’s expression for this spell to work? The text is a bit ambiguous, paraphrasing: The spell can be cast at range. The caster just needs to be close enough to see the target’s expression. Personally I like the idea of masks, hoods, helmets, and illusions providing protection from the spell. Also, could Dim light be a factor for casting and Darkness make it impossible to cast?
Yes to all, at least IMO. Not a big deal if folks want to interpret it differently, though.