Oops, sorry Cam - that 14 hours turned into something like 3 days. No I haven't been at work all that time... but have had lots going on.
I think the major problem with this one is that there is very little anticipation in both the movement of the character and, in a more general sense, the 'narrative'.
By anticipation of movement I mean what happens just before an action is carried out, at prepares us for the action about to happen. Like, if you throw a ball you first need to pull your arm back to gain momentum. If there is no anticipation in an animation it can make it look stiff and unnatural. If you watch people standing up from a chair - most of the time you'll see a shift of weight and people will rock backwards before they lean forwards to gain momentum for the lift out of the chair. This doesn't happen in your anim, he just goes from hunched to standing - which makes it look quiet awkward and unexpected.
As for the anticipation of the narrative - you are getting there... that lean forward to listen to the box lets the audience know that something is going to happen

But that is kinda lost when he stands up. It's difficult to explain why but I'll try...
First because there is no real 'reason' given as to why he stands up (not that there needs to be a reason - but there should be more of an exaggeration in the body language to convey anger or frustration - or some other inner dialogue)
Secondly the actual standing action runs straight into the following and final action (ie the punchline), because he very slowly raises his hand to his chin. That action needs to be done and dusted before we (the audience) can begin to anticipate the next. That's where a nice long pause is needed... so we know something will happen, (but we don't know what) and the longer that pause or anticipation is, the more sudden your action can be
Anyhoo - don't take all this as a negative thing. There are a lot of positives and improvements too in this anim. You've certainly got the idea of secondary motion... from the punch to that slide on the floor is very nice indeed.