That's looking good already!
What you could do in order to push it a bit further is by offsetting a few components. For instance, the first pose, in order to get rid of the symmetrical look, vary the eyebrows and the mouth shape. The first look is a bit generic.
Then, for the take, right now everything is moving at the same time from x1 to x2. Think about what he's seeing and the fact that he's seeing something means that his brain needs to deconstruct the information first. Your guy could get slapped from behind his head and the way he goes down would work. But in a take, give it a few frames to anticipate the down. So his eyes could widen for two frames, same with the mouth, etc. He would go from the current "happy" to an anticipation with a face reading "What did I just see?" and you could lift his body up a bit, so that the body does a little anticipation as well.
Then on the down, since it's pretty fast, you could raise the eyebrows as the head goes down, as if they are dragging and overlapping (so you'd lower the brows when the head goes up again; kinda what you have but you could delay the frown a few frames). On the head down you could also stretch the head and squash it around the x6 area. I'm talking about feeling the squash/stretch, not really seeing it, it's a more subtle application of that principle.
Track the spacing and arcs of the nose. On the way down and up it's following almost the same path. You could exaggerate the arc a bit more, same during the settle where the nose path would be a little loop as it settles. Nothing crazy, but a bit more pushed than what you have now.
The ending works well and the facial expression is more asymmetrical than the beginning one.
Hope that helps!