You'll be faced with major differences in the way that you think about life in general. You might stubbornly insist that yours is the best or even only way to look at an issue; this might actually be a mask that covers the fact that you know you're not necessarily correct in your thinking, but you're just not willing to admit it. This aspect poses the opportunity for each of you to grow immensely in your view of the world -- if you can convince yourselves to listen to each other and respect your individual viewpoints instead of shutting each other out.
You'll definitely learn something, and you could even find that your opposing viewpoints are actually complementary. You may even decide that this is part of what brought you together in the first place -- instinctively, you knew that each of you had something the other lacked!