Well Tsipras:

• Is not promising to keep Greece in the eurozone. He's claiming that SYRIZA's road is the only road that offers a chance to remain in the eurozone. The other road leads to total societal collapse before 2013
  
• He is suggesting a moratorium on debt, not debt cancellation, pretty much on the terms that Germany got in 1953 (offered by Greece among others)
  
• He does not promise to double minimum wage but rather: a. Return it to the levels it was in March 2012, and b. Re-establish a collective bargaining system.
  
• Will roll back pensions to where they were in March 2012, if I'm not mistaken
  
• Note that the 4 month primary deficit for 2012 was something like 18 million euros, only (although the prognosis is grimmer for the rest of the year). True there are arrears of internal debt to suppliers, tax returns etc, but these won't be paid soon anyway...

Basically Tsipras is saying that Greek society will not and cannot continue on the road of the memoranda without exploding soon. And he is offering the EU the only way out of a dead-end policy.

See this interview of Varoufakis in Die Zeit for more (in German, I haven't read it in the original but in Greek translation)

The road of excess leads to the palace of wisdom - William Blake