This is far from over. Acting too quickly or rashly would be as big a mistake as not acting at all.
I believe that this invasion was like a message to the world. It was basically a "Hello, Russia's still large, and on this continent, still in charge" kinda message, meant mostly to the West. It also showed the Russian people that Putin could face down the U.S., and NATO as well, by doing this. I honestly think our best play would have been to have moved in and slapped him down ASAP. It would have lost him face with his gov't., and IMHO, we would have been rid of the worst of the old Soviet Hard-liners, because he most likely would have taken the blame for what would have been a fiasco for Russia (if we had responded strongly.)