They say opposites attract. They most certainly do. But how desirable is that? In my opinion, it depends.
Many a love stories begin with totally opposite people hating each other and eventually falling in love. Sounds romantic. But is it sustainable? Depends on the kind of differences people have. From personal experience I have realised that it makes sense for two people in a relationship to have common hobbies, interests, likes and dislikes; but opposite behavioural characteristics.
The similarity of likes and interests will always give them something to do, see, experience and enjoy together without issues. For example, when both people are non vegetarian, or love travel, life would be fun together.
However as far as behaviour is concerned, they should complement each other. If one is impulsive, other should be calm. One has a quick temper, other should be patient. One is talkative, other should be laconic. In this way they will have a perfectly balanced relationship with each other and with everyone else outside.
Of course you may still fall in love with a completely different or exactly same person in all aspects: and it would be your maturity and the strength of your love that would see the relationship through till the end of life. If you have such a relationship, God bless you! If you are one of the lucky ones to have a partner who balances you out, great going and good luck! :)