It must guide new players to do the right thing. "Cancel the replay" is clear to us; is it clear to the new player? It will be negative wording (cancel the unwanted replay) and forces you to first understand what the replay ist.
It's probably a wash because it still says explicitly "Replaying." and it's moderately easy to guess what that means. I'll have to user-test "to cancel the replay" vs. "to play" with complete newbies.
yoyoz considered the replay a bug and wanted to build NL from source to kill the replay. His wording is indeed that some actions are "replayed" and he didn't want that. "Click to cancel the replay" would have been clear for him.
Months ago, I had "Replaying. To play yourself, click into air." I cut the seemingly useless "yourself" for brevity. If
you click, who else should be playing, other than yourself? I think I put the "yourself" to contrast with the replay's playing.
The idea behind "to play, click" is also to tell the newbie that he
is not playing. This is an underhand explanation of what the replay does, it plays for you.
Click without context is always left-click, and shorter. Fewer words are easier and more enticing to read. I believe the lack of precision here doesn't mislead the newbie. To fail this, you'd have to right-click because that's somehow more natural, then be confused, then still never try left to click.
But I'm open to be convinced otherwise. Again, the goal is to get newbies to read the text, and get the cancelling right.
There is "click" elsewhere. E.g., in the replay tweaker (filmstrip button during play) when the replay is empty, the text will tell you to "Click some lix. Later, tweak" and it too means left-click. Do you want all of those changed? Or is the consistency sufficient (they all mean left-click)?
-- Simon