Opposites may attract, but in good storytelling they repel.
However, a well-rounded antagonist does not simply seek to quash every forward movement of your protagonist. In fact, from your antagonist's point of view, if she is written well, she will consider herself the hero of the story. That's because to her, she is the hero of her particular tale.
As I sit and watch the New England Patriots take on the Miami Dolphins in Monday Night Football, I'm reminded of the best example of equal and opposite forces, trying like heck to get what they want: to win the game. From the Pat's point of view, they deserve to win; yet Miami feels they deserve to win. But there can only be one winner. And do we viewers care? Judging from the cheers and jeers from the fans, I'd say we're vested in the outcome of this particular tale.
So not only must you make sure your audience empathizes with your protagonist, but you must give your antagonist more than just a two-dimensional personality, so that even if for only a moment, we can see from the antagonist's point of view. We may not agree with your antagonist, but perhaps we can comprehend his actions and his do-or-die goal.
Storytelling is about keeping us absorbed in your tale. Developing good, well-rounded characters is a sure bet that we'll care...and we might even stay with your story till the final FADE OUT.