Complexity and enjoyment

Rhythmic complexity is a quality I've always enjoyed in music.  It's not necessary, but as a bassist and wannabe drummer, I've always paid particular attention to rhythm (both from within the rhythm section and without). 

One factor that I feel is responsible for a lot of complexity and (for me) personal enjoyment in music is rhythmic in nature. If a piece of music contains unusual time signatures, or multiple voices playing in differing rhythms, this makes it more complex. Not only do I find the complexity enjoyable, I like the "layering" that results from the interaction of these different rhythms. In general, the presence of many interlocking layers makes music both complex and enjoyable for me, but the rhythmic component of this is one of the most influential aspects.

I would say that complexity (to a point) can hold a listener's attention, because in the absence of a complex arrangement, the music can become either predictable or sparing, both of which can be boring. This isn't to say that sparse music is necessarily boring, because there is a lot of good sparse music as well, but  the presence of complexity can provide enjoyment of its own.

What qualities do you feel makes a song complex to create?  Are these the the same qualities you seek for auditory enjoyment?  Just curious to hear what the prog community comes up with...