After Jesus showed up, the Old Testament basically became a way for Bible publishers to keep their word count up.
Of course, just because Jesus replaces the Old Testament doesn't mean that you should necessarily skip it. That would be like skipping Batman and Robin just because the story starts over in Batman Begins. The important thing to realize is that both the old and new stories are about an all-powerful being trying to rid the world of evildoers, only in the new one The Batman can eat pork.
