What's there already is really good, but the problem is there's absolutely no melodic line.
Basically, this is a very well written accompaniment, but without anything running over the top it just sounds incomplete.
If you put a saxophone (or other instrumental) line over the top, theres a lot of potential for this to be awesome, but until then it just doesn't quite sound finished.

Of course it's your piece and I don't know your intentions, it could still have its uses as a background loop or such.