He & his party are the only things standing between Greece and a total neoliberal revamp of the country akin to Chile 1973-82 or the former Soviet republics after 1989.
Just look at the privatisations already happening atm on order of the EU, there's no sensible plan whatsoever, even profiteable state industries or valuable public assets (lands, mining rights, etc.) are being sold at a cut price to speculators.
Also, the party's main rival, the conservative ND is exactly the pinnacle of the corrupt political class that ruled for decades and is largely responsible for getting Greece into this mess.