I beg to differ. Thomas Aquinas wrote that God is not “a being,” but rather “being” itself. This is very similar to what meltzerboy wrote in the OP. Perhaps this is what God meant when he described himself to Moses as “I am.” (Exodus 3:14).
Father Robert Barron speaks at length of this in his video series, Catholicism (and the companion book of the same title). Here is a quotation from the book:
Following the prompting of this conversation between Moses and God, the mainstream of the Catholic theological tradition has tended not to refer to God as a being, however supreme, among many. Thomas Aquinas, arguably the greatest theologian in the Catholic tradition, rarely designates God as ens summum (the highest being); rather he prefers the names ipsum esse (to be itself) or qui est (the one who is). In fact, Aquinas goes so far as to say that God cannot be defined or situated within any genus, even the genus of “being.” This means that it is wrong to say that trees, planets, automobiles, computers, and God—despite the obvious differences among them—have at least in common their status as beings. Aquinas expresses the difference that obtains between God and creatures through the technical language of essence and existence. In everything that is not God there is a real distinction between essence (what the thing is) and existence (that the thing is); but in God no such distinction holds, for God’s act of existence is not received, delimited, or defined by anything extraneous to itself. A human being is the act of existence poured, as it were, into the receptacle of humanity, and a podium is the act of existence poured into the form of podium-ness, but God’s act of existence is not poured into any receiving element. To be God, therefore, is to be to be.