In short, it was just the sort of speech that was bound to infuriate hawks such as Senator McCain who called the president's response to the fighting in the Ukraine "cowardly." At the same time, it wasn't the kind of speech likely to inspire the president's supporters either. What would probably stir people more might be a Rooseveltian ("day that will live in infamy") or Churchillian ("fight on the beaches") type of response to the outrageous act of violence that appears to have been committed by Ukrainian separatists with the help of their Russian patrons.
But remember that both Roosevelt and Churchill made their stirring remarks in an effort to whip up national resolve to fight and defeat an enemy that had already brought war to their shores. Our side needed to be mobilized for all-out war. President Obama's much harder challenge is to stir up the desire for peace, not only to avoid a military confrontation with Russia, which no responsible person wants, but also to reduce tensions in the Ukraine. He faces a similar task dealing with the situation in Gaza.
Even though the United States supports the Ukrainian government in its struggle against the separatists, and supports Israel in its struggle with Hamas, the president was attempting to play the role of mediator. To do that you have to emphasize the goals of fairness and impartiality. You have to be careful not to exaggerate threats or to accuse the enemy of anything more than you can prove. You have to give your adversary a face-saving way out of a dangerous situation.
Laying out a path to peace in this way is far from easy. It's certainly not cowardly. The challenge for the president, as for any would-be mediator, is to persuade the parties that they can accomplish their goals more readily by peaceful means, and that further retaliation will only make the situation worse. Perhaps to make peace, we have to talk less about the grand designs and historical claims of the respective parties, and turn the talk toward such mundane topics as implementing a ceasefire, conducting an independent factual investigation of plane wreckage, restricting arms shipments to the combatants, and calculating the damage to lives and property inflicted by the scourge of war. If the parties can focus their effort on cleaning up the mess, maybe they will consider less destructive means of managing these conflicts.