St. Thomas Aquinas' metaphysics can best be described as?

This is quite a question, and I don't know that I can short/summary the formula, but there are a number of sights that detail it;

You might begin with;

http://www.innerexplorations.com/philtext/the.htm

http://www.iep.utm.edu/aq-meta/

http://plato.stanford.edu/entries/aquinas/