It sounds like the basic plot is the same (Fisk running for Mayor, etc), so they're keeping some stuff but not everything. They wrapped filming now, but started in January, so they didn't scrap all the footage but are retooling it. The biggest difference seems to be A: the return of more of the original cast (since it was originally just Matt Fisk and Frank returning) and B: adding more serialized elements whereas the previous one was more episodic. They completely reshot the first episode, parts of the episodes already filmed, and completely redid the final two episodes (which they hadn't gotten around to begin filming in the first round of shooting)