The God we serve is a God of love. When we receive a full revelation of the love lavished to us through Jesus Christ, we will - in response to this love- act in love towards others. The Bible even tells us that God's perfect love is what enables us to even love our enemies.
The Christian faith is one that is founded on the foundation of love. We are saved by love, preserved by love and motivated by love. To act in any way apart from the basis of love is far from what God wants us to do. John 13:35 tells us, "By this all people will know that you are my disciples, if you have love for one another."
But does God's call and command to us to love unconditionally mean that we're supposed to be nicer? Well, it really depends on how you define "nice." People have this notion of nice-ness as wearing a smile all the time, shouting "Hallelujah" even when troubles come and blessing those who take advantage of us. I don't believe that God calls all Christians to fit this stereotype although many Christians do behave this way and God is pleased.
But being nice goes beyond external behaviour and perpetually jubilant expressions. The psalmist David, for instance, was considered to be a man after God's own heart yet many of his psalms were depressing at the same time as honest. Jeremiah was one called by God even before he was even born, but he is also the prophet who cried out, "O Lord, you have deceived me, and I was deceived." (Jeremiah 20:7)
God does want nicer Christians in the sense that we love unconditionally and act in meekness and humility. Matthew 5:5 tells us, "Blessed are the meek, for they shall inherit the earth." Receiving the Spirit of God brings forth a fruit of love, joy, peace, patience and a lot of nice characteristics.
Matthew 5:39 also tells us, "But I say to you, Do not resist the one who is evil. But if anyone slaps you on the right cheek, turn to him the other also." God does want nice people who act in love, but being nice doesn't always mean being a push-over or letting people take advantage of you.
Jesus also calls us to be stern and firm, often being wise as serpents though being innocent as doves (Matthew 10:16). He calls us to 'violently' take hold of God's promises (Matthew 11:12) and to even resist the enemy (James 4:7). God wants us to be nice, but He also wants us to be strong, and strong people can act in love just as gentle people would.
