IGN compiled five ways the Judas Contract has changed DC Comics.
They may have given it too much credit, but here's the closing excerpt:
Without The Judas Contract, it's debatable whether DC would have gone forward with other controversial storylines like The Death of Superman. Terra's betrayal and subsequent death paved the way for similarly shocking developments like Batman's back being broken or Hal Jordan going insane and destroying the Green Lantern Corps. You can even see the DNA of The Judas Contract in more recent stories like Identity Crisis (which also happened to feature sordid sexual revelations about a Teen Titans villain and Deathstroke laying waste to an entire team of superheroes).