I have been a composer too long to see that comments like 'nice' or 'excentric' are not very fertile for development.
So, if somebody asks my opinion, I analyze things and come with a report. Plus, Zero and Minus.
Structure indeed.
Since analog electronics this is called the 'envelope' of the song. The form of intensity in time you choose.
Also called the 'tension-curve'. How do you build up, lay back a bit, building up again, introduce the coming end, etc.
The drawback with electronic sound is the danger of things getting too long or with too much repetitions, because it's so easy. As long as there is electricity, it can go on, while you would get quite exhausted blowing a flute for 45 minutes.