Don't for an instant allow yourself to believe that i believe the Federal Law outlawing marijuana growth and distribution is a good one. But unfortunately, I have to agree with the justices who say that a state law legalizing marijuana is legal in any fashion MUST violate the federal law and, therefore, violates the "supreme Law of the Land." The Constitution is unambiguous on this point (you might even say it's rather specific!): "...the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding" (VI, clause 2).
I personally hope for the day where either the federal law is changed (which I doubt will happen) or a constitutional amendment to somehow exempt cannabis from Article VI. Until one of these happens, though, growing and selling pot is unambiguously a violation of federal law.