What does creationism lack that makes it not a science?  Everything.

  1. It lacks any mathematical models, even something as simple as Mendel's
     laws.  When creationists do attempt some math (as in their probability
     arguments) they produce rubbish that should embarrass a high school
     student.

  2. It has no basic argument that gives a unified explanation of a variety
     of phenomena.  The closest candidate is Noah's flood.  But for a flood
     to produce phenomena, by "hydrodynamic sorting" or whatever, it has to
     work by physical processes that have observable consequences and
     mathematical models.  The detailed analysis that is the hallmark of
     real science is absent.

  3. It lacks any contact with any science. It is in conflict with biology,
     paleontology, geology, physics, and astronomy at all points.

  4. It does not make predictions which are testable.  The essence of
     creationism is that the world is the way it is because that's the
     way god made it.  This makes no prediction about the outcome of an
     experiment and any result is consistent with the theory.