The upness controls the "embellishment" of the harmony and the melody. If upness is high, the notes tend to go more up the scale and so on.
I agree that the MIDI is quite terrible, but one can build a better soundbank perhaps?
The music reacts slowly because it generates a whole measure at a time and I am simply appending a track with events which gives a certain lag. Also, there is a smoothing factor to prevent sudden changes. However, all of these problems will be taken care of in future iterations.
Have any of you tested cgMusic? (edit: I saw that you already have discussed this in the forums. Sorry :) )
I ask because my next step is to try and make adaptable versions of some of the scripts in that program.