[Alan]

Was the Soviet Union a Marxist country? Why or why not?

In the beginning it was, and ideologically Lenin really was a true successor of Marxist thought.
After the October revolution, political power was indeed located at the soviet level, and that's how it should have remained. However, different factions began to struggle (even before the Bolshevik v Menshevik split) which caused a civil war within the country. This gave a new opportunity to the royalist army to regain power, backed by numerous European countries.
Lenin became more authoritarian as he felt the need to consolidate his power to better fight the White Army. During and after that, he also persecuted the more openly dissenting groups within the Soviet Union, such as the anarchist Makhnovtchina in the Ukraine. Trotsky criticized Lenin for this, saying that the centralization of authority only obstacles the proletariat instead of helping them, but I don't think he would have been any better, and he was still the commander of the Red Army during this time.
After the civil war, being fought in urban environments, and the popular Red Army being composed of working class volunteers, the industrial working population of the Soviet Union was drastically reduced (20 million casualties). Lenin himself began a program of further centralization, going so far as to moving peasants to cities to become industrial workers. This offered them better living standards, but they lacked a proletarian upbringing; Lenin basically artificially created a new proletariat, an untrained working class.
He also compromised with the royalist bourgeoisie, giving them several privileges and restoring their business positions, so as to restart the economy.
From a political science point of view, these are all smart and necessary decisions for a leader of a country to do in these circumstances. It would be naive to think he should have remained true to his ideals against the grey reality of the situation. But at the same time it is clear the Soviet Union's infrastructure was far from being a Marxist infrastructure. At best, as long as Lenin was alive, it was a command economy nation hoping that someday, somehow, it could become a free socialist nation.

How can you like Obama?

Ah ha! I saw that!
Lesser of two evils I guess. He's not that bad anyway. In our circumstances and under the rules of this game, he's a pretty good president.

Was Nazi Germany a Marxist country? Why or why not?

Not at all. It is not Marxist at all, and I'm not saying that simply because I'm a Marxist. The first people Hitler targeted were communists, and the Nazi party's economical ideology was explicitly geared towards eliminating any trace of communism in Germany.
However, Nazi germany still had a command economy, so it is actually quite legitimate to think of fascism as being in a certain manner socialist, especially compared to a free-market economy. But this command economy is called corporatism: corporations are boosted by the government to compete in the free market, while German workers have limited rights in their working environment, so as to 'not harm the economy'
Prohibiting free press, strikes, and unionization are antithetical to Marxist socialism put into praxis (that goes to Veneuela and Cuba too)

Did Marx make any predictions? If he did, how did those predictions turn out?

Marx made a lot of predictions. Most of the predictions he made about capitalism are quite correct. One of the best examples is how capitalist production necessarily stalls periodically (recessions and depressions) and these only get bigger and bigger. He also dipped a little in the idea of stable capitalism being temporarily possible through colonialism (a theory further expanded by Lenin on Imperialism, the Highest Stage of Capitalism)
And he even went against a common socialist idea in his time. Socialists, particularly Lasallean socialists, believed in a concept called the Iron Law of Wages, which said that despite temporary victories, wages eventually tend to fall to the bare minimum necessary for subsistence. It is obvious that this looks attractive from a socialist point of view: it proves how unforgivable evil capitalism is. But Marx proved that this "Iron Law" does not exist. There are legitimate reasons to fight against capitalism, so we should not believe in a false 'law' that is proven to be mistaken just to make capitalism look less redemptive.

On the other hand, Marx's magnum opus, Das Kapital, is clearly outdated and very wrong in many assumptions even in his time, like the tendency of the rate of profit to fall. There is speculation that Marx didn't finish Das Kapital because he realized he was wrong all along.
Numerous other Marxist economists have amended, contradicted, or completely abandoned Marx's theories on capital in the name of better theories that explain the workings of Marxian economics and the implications of capitalist economics in today's world.