It is quite common that Puritans get a bad rap. Mencken’s quip above expresses the sentiments of many a poorly informed soul in that regard.
Were there self-righteous, overly pietistic, religionistic blowhards filled with quasi-spiritual smuggery among the Puritans? Yup. Just like there are today (and always have been) in every branch of the Church. But is that a legitimate broad brush with which to paint the entire crowd? Nope. Not even close.
In fact, if you can read the following excerpt from my favorite of the Puritan preachers – John Flavel, and still come away with such a dim view – then I guess I have no means whatever to change your mind. No evidence will suffice.
But for me – God give me the heart that can pour out this kind of worship, whether in public or in private, in preaching or in prayer, and I will die a blessed man. This is what Puritan worship sounds like in the midst of a sermon. And this, is high stuff indeed.
Of Jesus Christ, our Puritan Preacher waxed:
“He is a sun of righteousness; a fountain of life; a bundle of love. Of him it might be said in that day, Here lies lovely Jesus, in whom is treasured up whatsoever an angry God can require for his satisfaction, or an empty creature for his perfection; before him was none like him, and after shall none arise comparable to him. “If every leaf and spire of grass,” (saith* one,) “nay, all the stars, sands and atoms, were so many souls and seraphims, whose love should double in them every moment to all eternity, yet would it fall infinitely short of what is due to his worth and excellency. Suppose a creature composed of all the choice endowments that ever dwelt in the best of men since the creation of the world, in whom you find a meek Moses, a strong Sampson, a faithful Jonathan, a beautiful Absalom, a rich and wise Solomon; nay, and add to this, the understanding, strength, agility, splendour, and holiness of all the angels, it would all amount but to a dark shadow of this incomparable Jesus.”
“Who ever weighed Christ in a pair of balances?” saith another. “Who hath seen the foldings and plaits, the heights and depths of that glory that is in him! O for such a heaven, as but to stand afar off and see, and love, and long for him, while time’s thread be cut, and this great work of creation dissolved!—O, if I could yoke in among the throng of angels and seraphims, and now glorified saints, and could raise a new love-song of Christ before all the world! I am pained with wondering at new opened treasures in Christ. If every finger, member, bone and joint, were a torch burning in the hottest fire in hell, I would they could all send out love-praises, high songs of praise for evermore, to that plant of renown, to that royal and high Prince, Jesus my Lord. But, alas! his love swelleth in me, and finds no vent.—I mar his praises, nay, I know no comparison of what Christ is, and what he is worth. All the angels, and all the glorified, praise him not so much as in halves. Who can advance him, or utter all his praise?—O, if I could praise him, I would rest content to die of love for him. O, I would to God I could send in my praises to my incomparable Well-beloved, or cast my love-songs of that matchless Lord Jesus over the walls, that they might light in his lap before men and angels!—But when I have spoken of him till my head rive, I have said just nothing; I may begin again. A Godhead, a Godhead, is a world’s wonder! Set ten thousand thousand new-made worlds of angels and elect men, and double them in number ten thousand thousand thousand times: let their hearts and tongues be ten thousand times more agile and large than the hearts and tongues of the seraphims, that stand with six wings before him; when they have said all for the glorifying and praising of the Lord Jesus, they have spoken little or nothing. O that I could even wear out this tongue in extolling his highness! But it is my daily admiration, and I am confounded with his incomparable love.”
Search out this wonderful God until you can stand no more visions of His beauty, glory and grace.
 Flavel, John. 1820. The Whole Works of the Reverend John Flavel. . Vol. 1. London; Edinburgh; Dublin: W. Baynes and Son; Waugh and Innes; M. Keene.