What gives gunplay impact?

One of the main criticisms I've been seeing about Anthem is that its gunplay isn't impactful. This got me reflecting on examples of the obvious way to add punch to gunplay, headshots. I remember are the headshots in Spec Ops the Line feeling great. I'm sure there many other examples of satisfying headshots, which I would love to hear. However, I've been struggling to articulate why hitting headshots or similar weak points feels good in some games. Is it the sound? Some visual flair? What other factors add impact to a shooting mechanic?