Do you think it is in the DNA of Calvinists to be disgruntled? After all we have a commitment to always be working to reform church and culture. So we are inclined to look at a situation and focus on what needs to be fixed and not what is working.I do think that a worldview that began with protest and reform does tend to emphasize the negative. Nonetheless, the core of the scripture that Calvinists confess is that God created the world and called it good, and Christ ultimately triumphs over sin. The basic message of Christianity from beginning to end is pretty positive, and Calvinists embrace that message.
I think one of the reasons the Calvinists tend to be so critical is that we find it exasperating that other worldviews do not see the good order God made in the world. Calvinists are stewards of the world in order to work with and bring out the good order that the sovereign God made.
I have toyed with the idea of writing The Happy Calvinist. That happiness is chastened by the knowledge of sin and the Fall, but nonetheless remains cheerful knowing that God triumphs, first and last.