The party system of a successful communist revolution in Germany (POD would be, that the SPD rejects World War I instead of rejecting it):
Sozialdemokratische Partei Deutschlands (SPD):
Social Democratic Party of Germany
Perhaps the party that is the closest to its real-life counterpart. They follow the politics of OTL 50's with a great touch of Willy Brandt's politics. So they are naturally advocating a nationalized, state-planned economy, but good relations with its neighbours.
Kommunistische Partei Deutschlands (KPD):
Communist Party of Germany
In TTL's 2010, it's the melting pot of different communist ideals. No movement has a real majority. There are Marxists, Leninists, Trotskyists, Maoists, small Anarchist and Stalinist wings and some more. While there are many conflicts inside the party of its ideological direction, they strangely seem to find a consensus every time. They prefer grassroots democracy over parliamentary democracy, and want to go on a more confrontational stance towards capitalist nations. Otherwise, there aren't much differences compared to the SPD.
Soziallibertäre Partei (SLP):
Social Libertarian Party
They formed out of the Anarchist wing of the SPD. But they don't reject the state per se. They want to bring Germany further to Anarcho-Communism, but they want to keep the state (Unlike abolishing it), because they realized that certain administrative duties can't be relegated to the people. Still they want to achieve as much self-determination for the people as possible.
Die Grünen:
The Greens
They are like OTL 1980's Greens. They didn't turn into realpoliticians, but stayed idealistic. Perhaps you can also compare them to the Social Ecology Union from Jello_Biafra's TL on this forum.
Zentrumspartei/Christ-Sozialisten (Z/CS):
Centre Party/Christian Socialists
Originally there were two parties. The catholic Centre Party and the ecumenical Christian Socialists. While the Centre Party represented conservative, catholic beliefs, the CS stood for liberal, socialist christianism. Both parties wanted to present a home for christian people, who were confused after the revolution. But they ended up rivalling each other in their quest of getting more christian votes than the other party. But after the Second World War, both parties formed a tight alliance. While they aren't de facto a single party, they form a united faction in the Volkstag and they don't compete against each other in elections anymore. Today they tend to agree with the SPD or KPD on most economical issue, but they want to preserve Germany's "christian legacy". The "positive aspects" that is.