I would define a good superpower as one with a vested interest in preserving and spreading the freedoms and peace that we enjoy so much in the western world to the world as a whole.
I would define a bad superpower as one that executes political dissidents without trial, runs a total police state and enforces its will violently to gain direct control over other nations.
Here is where the distinction get's very blurred, can a nation with good intentions engage in bad activities to uphold the greater good? It is a question that one struggles with and creates a great deal of dilemma, how much action is to much action? Is inaction in the face fo violence criminal?
I would say that some action, for example war in Iraq is a good thing for the people of Iraq and the Middle East as well as the Western World in the long term, the benefits (if done properly) will be the introduction of liberal (critical here, distinguishes between simple democracy as a liberal democracy has strong foundations of human rights and freedom) democracy to a place where it has never existed before, if sucessful it will be an example of a positive resolution through millitary action. Millitary action can bring about democracy, we only need to look to the former Yugoslavia to see intervention is not an inherently bad thing if done properly.
A bad action would be the subversive overthrow of Carlos Allende in Chile, this was an action that was given tacit support by key players in Washington and is an example of abusing power. This type of action was wrong and I strongly believe it was not a failure of democracy, rather the concentration of executive power gone amok.
Liberal Democracy is allways a balance between two things, freedom and security. We must give and take a little of each depending on the demands being placed upon it. For more security we will need to remove more freedons and likewise when we wan't more freedom we are sacrificing security.
The critical thing and this is a really important point about a liberal democratic system is that there must allways be oversight. In open society's there is allways oversight of actions and when that fails proper punishment follows, this distinguishes a "good superpower" from a "bad superpower". When you look at your totallitarian regimes there was never proper accountability for the crimes of the state as everyone involved was just a gear in a larger machine. When you have your Nazi Germany's and Stalinist Russia's millions of people were murdered in the name of progress or racial purity and nobody would pay for the crimes. The victims did not have a voice and the people themselves were helpless to fight against it as they became part of the system itself. This contrasts sharply to the liberal democracys of the world where when abuses of power occur responsibility is found out and people are held to account (either in court or at the ballot box) and the entire society works to fix the problem. For the past one hundred and fifty years we have seen the progress that liberal democracy can bring to the people of the world while other systems have failed outright.
I am not going to argue that the US is the greatest example of democracy in the world, it is not. It is however in the position to become a truly great power when it whole heartedly embraces the cause of freedom and peace around the world. I do not believe that a real peace may be achieved with dictators who will cut deals at the negotiating table while their people die, the abhorent abuses of human rights that occur in totallitarian societies must be stopped through whatever means at the disposal of the civilized world. If this means being tough on a political/diplomatic front then so be it, if this means having to enforce sanctions so be it, if this means war as a final option then so be it. I do not wan't to advocate some type of total war against the rest of the world but I do think that in some situations we shouldn't be afraid to use our power properly.
The use or abuse of power is at the core of the whole problem. How can one wield power without becoming corrupted by it?
This is another problem, one that I will certainly be considering before my next reply post. In summary - Good Superpowers do not opress people and will work hard to bring freedom to the world by eliminating totalitarianism from it. Bad superpowers opress the people and the power is concentrated within the top echelons of a select few.
I must apologise for the post's length and somewhat shallow nature however it is a really, really good question that is best discussed over a bottle of scotch and an entire evening.