What do you think of this argument for God?

[Nonpareil]

You should look at the real version of the Ontological Argument--every word is carefully defined. 

They're really not, but it wouldn't make a difference if they were.

Every ontological argument makes the same mistake - or, rather, they fail to do what would actually be necessary to prove their conclusion. They attempt to define "God" as "an entity which is necessary", but even granting that this definition is coherent (and it really isn't), it fails to actually establish that it applies. At best, it is valid, but not established as sound, and becomes bare assertion.

Other issues depend on the specific version of the argument you wish to back.