Well, they promised freedom from austerity and now they're going to get it, good and hard:
Alex Tsipras, the young, charismatic leader of Syriza, is an avowed leftist (his son, Ernesto, is reportedly named for Marxist revolutionary Ernesto “Che” Guevera) and the party’s most likely candidate for prime minister. Tsipras has made it clear that any new government under Syriza—an acronym from the Greek words meaning “coalition of the radical left”—will “renegotiate” the loans extended to Greece by the EU, the IMF and the ECB since 2010 in order to preserve the euro. Those loans—now totaling some 175% of Greece’s GDP—were conditioned on austerity measures that Tsipras has declared intolerable.As this Atlantic article notes, the options for the Eurozone "troika" are to write down Greece's debt - and give other PIIGS a blueprint for forgiveness - or kick Greece out of the Eurozone. It's gonna be interesting.
While the Greek economy is growing moderately, and Greece is likely able to continue its debt service under existing austerity measures, a Syriza-dominated populist government would likely bring about an economic crisis worse than the one Greece and the Eurozone saw in 2010.
Extra - Or can Tsipras pull of the "Lula pivot"?
More - Daily Mail: "EU braces for catastrophe."