The Ontological Argument as Proof of God

The Ontological Argument is seemingly one of the more popular arguments which Rationalistic theists like to employ in trying to prove the existence of God. The rudimentary version, as written by Anselm, essentially goes like this: -P1- One can conceive of something which is "Most Great" -P2- Existence is greater than non-existence --Conclusion--> the "Most Great" thing which was conceived of Must be existent, as existent things are more great than non-existent things. It has been around for quite some time, and has been controversial, and so attacked, since it's inception, but it still seems to be kicking through people's minds a bit. My goal now is to show that it shouldn't have ever had any kick in the first place :) - - - Now, although this argument has received much critical attention in it's history, and there have been several different kinds of objections to it, I believe that the most striking problem with using this argument to try to prove the existence of God has not been paid enough attention to. For what is most immediately clear (with this formulation of the argument) is that it doesn't make what is intended to be it's reference to God clear enough to show that what's purportedly been proven is God, rather than something else. Additionally this lack of clarity in regard to what it means to conceive of something "Most Great" undermines the merit of the argument he actually makes. In order for his argument to hold water he needs to show that "greatness" is an objective standard. He needs to show that the conception of "something that is Most Great" does not differ from person to person, for, if it were to, then the argument would purportedly prove the existence of multiple different "Most Great" things, and would be nonsense. Anselm suggests that we can conceive of something that is Most Great, but doesn't, within this argument, explain what "Most Great" means, beyond (his conclusion) that it must include existence, as he says (-P2-) that existent things are "greater" than non-existent ones. So, the only characteristic his "Most Great" has, to this point, been suggested to have is existence. "Greatness" has yet to be objectively defined, and why existence is necessarily characteristic of it (-P2-) has not been explained. Given that only this one characteristic of "Most Great" has been suggested, it seems that by "Most Great" Anselm could have simply meant conceiving of something "Most Existent" But then his argument would only prove that something which is "Most Existent" exists. - - - So, in order for this argument to be legitimately used in an effort to prove the existence of God, and avoid being taken as either uselessly tautological, or being so vague as to turn to nonsense through purportedly proving multiple different "Most Great" things; the term "Greatness" needs to be shown to be an objective standard, and "Most Great" needs to be shown to be the equivalent of "God", which can only be done by explaining why the characteristics of God are (according to that necessary, objective, standard) "Most Great" {the "characteristics of god", for the purposes of this debate, including Omniscience, Omnipotence and Omni-Benevolence} - - - I do not believe that this argument can be satisfactorily supplemented in such a manner, and would love to debate it (or my above evaluation of it) with a willing opponent.