From Salon.com:
Mark Twain on God--excerpts from his memoirs.


It isn't really news that Mark Twain hated Christianity.  His collected writings on the problems of Christianity can fill a whole book.
But, whether it's new news or old news, the excerpt Salon printed is still worth a read.  It reminds me a lot of Thomas Paine's style in The Age of Reason.
Which I suppose is not surprising because Mark Twain was a big fan of The Age of Reason (W).

Our Bible reveals to us the character of our God with minute and remorseless exactness. The portrait is substantially that of a man—if one can imagine a man charged and overcharged with evil impulses far beyond the human limit; a personage whom no one, perhaps, would desire to associate with, now that Nero and Caligula are dead. in the old Testament His acts expose His vindictive, unjust, ungenerous, pitiless and vengeful nature constantly. He is always punishing—punishing trifling misdeeds with thousand-fold severity; punishing innocent children for the misdeeds of their parents; punishing unoffending populations for the misdeeds of their rulers; even descending to wreak bloody vengeance upon harmless calves and lambs and sheep and bullocks, as punishment for inconsequential trespasses committed by their proprietors. it is perhaps the most damnatory biography that exists in print anywhere. It makes Nero an angel of light and leading, by contrast.

We brazenly call our God the source of mercy, while we are aware, all the time, that there is not an authentic instance in history of His ever having exercised that virtue. We call Him the source of morals, while we know by His history and by His daily conduct, as perceived with our own senses, that He is totally destitute of anything resembling morals. 
We deal in a curious and laughable confusion of notions concerning God. We divide Him in two, bring half of Him down to an obscure and infinitesimal corner of the world to confer salvation upon a little colony of Jews—and only Jews, no one else—and leave the other half of Him throned in heaven and looking down and eagerly and anxiously watching for results. We reverently study the history of the earthly half, and deduce from it the conviction that the earthly half has reformed, is equipped with morals and virtues, and in no way resembles the abandoned, malignant half that abides upon the throne. We conceive that the earthly half is just, merciful, charitable, benevolent, forgiving, and full of sympathy for the sufferings of mankind and anxious to remove them. Apparently we deduce this character not by examining facts, but by diligently declining to search them, measure them, and weigh them. The earthly half requires us to be merciful, and sets us an example by inventing a lake of fire and brimstone in which all of us who fail to recognize and worship Him as God are to be burned through all eternity. And not only we, who are offered these terms, are to be thus burned if we neglect them, but also the earlier billions of human beings are to suffer this awful fate, although they all lived and died without ever having heard of Him or the terms at all. This exhibition of mercifulness may be called gorgeous.