Okay simon... wow... you've got a lot going on there!
Let me get some words back from you and that'll help me figure out where to focus.
Here is where I might focus if I were doing the work.
1. The most important part is the end... the big payoff. There are some pretty substantial areas for improvement here that are very similar to your earlier short. The off balance fall is not playing right and doesn't flow in the full scheme of things. We've just seen Fred do all kinds of jumping and dancing around and then... no payoff at the end. There is no motivating factor that suggests Fred would lose his balance and fall except if he knows the video is coming to an end so he falls because you animated him doing that. (Not good enough I say)
Here is a mild suggestion but it's only my exploration of what might happen... not a suggestion per se:
When he gets to his last cue and the music begins he might recognize the odd music... pause a beat.... shrug... and anticipate deeply as he begins to start playing again... as he overexaggerates his motion to the beat he then starts to lose balance in three stages... leg up... leg UP.... leg too FAR UP! Now he is off balance and can start to react as he is falling.
2. Progression/Transitions. While you can do this in post it's important to think about it now. The key to a good transition is to cut mid shot. Because you are starting with a new riff every few seconds this is a little more of a challenge but I believe it mostly means that you need to concentrate your transitional progresses on the fading out. This should be done via audio but I am more concerned with images here. Think a completely black image. Now think of a white dot somewhere in that blackness. That white dot is your focus and it needs to be on Fred. Everything else fades to black. If you are familar with the term Vignette... that's similar to what I am talking about. (This effect can be achieved in A:M but in many other programs as well).
As far as Progression goes you also want to think in terms of opposites and increments. Think for instance; cold and hot. What is your hottest part of the sequence (It probably should not be the final payoff... because it's a gag you are building up... building up... building up... and then go in the opposite direction). Out of all of the different pieces of music each has it's intensity and that intensity grows (in some form or fashion) with each shot. Usually you want that change to be unnoticed during the build up so that's why it's incremental. You start this in a way with the intro... everything is dark. But do this with your main section too... and then go intense and let it fade off in the third part. If this doesn't make sense... I can throw more words at it.
Edit: I just remembered an important tool of progression you can use for each of the music shots. For your consideration:
As each new piece of music begins start zooming in slightly with the camera (you can do this after all of your images are rendered... you don't have to rerender them again!). If more appropriate you can pan, tilt or shake the camera to capture the specific music you are on. Then as each new piece of music begins... BAP! You are back out and progressing back with the camera into the shot. The general rule: When thinking of progression in your scene where appropriate don't forget to progress the camera. Otherwise there will be less life in the sequence over all.
3. I smashed #3 in with two so I'll add this:
Minor quibble: I don't think the mop/broom standing up is going to cut it without something keeping it up there.
Possible Suggestion: Have Fred hold it as he decends but then push it upward as he goes down (this is an important element of animation... a secret... so don't tell anyone... as you animate one thing going one way, animate another going the opposite way. Shhhh... our secret). Now an important part of this mop going back up is that it doesn't get all the way back up. And when it runs out of energy it starts to fall down to the floor where it accentuates the end with your trademark bounce (seen in your last episode).
You've got the essence there now you need to work on the presentation and payoff.
What you've got now is looking good. Keep it up!