What are the main points to remember about the poem "Ozymandias"?

I would say that the transitory nature of existence is one of the critical points from the poem.  The ruler Ozymandias, self described as the "king of kings," is one whose statue is in a decrepit condition, set in a barren land.  The notion here is that during his rule, people might have seen him as a powerful king.  Ozymandias might have even seen himself as one of these rulers.  Yet, the possession of political power does not guarantee political immortality.  Rulers cannot be measured by solely their success when they rule, but must be assessed on the grounds of what they have done to ensure that their rule is lasting.  At the same time, this can be broadened to anyone who seeks immortality for its own end.  All artists could be subject to the fate of Ozymandias, seeking immortality in this life, but not accomplishing it after their time has passed.