Oliver Cromwell left no written opinion of Martin Luther, but people in his circle were keen to use Luther's writings to further their own aims. Meanwhile, John Milton and John Bunyan thought well of Luther though in general only a few translations of the German Reformer had been made into English.
The Puritan feeling for Luther was rather a cool one, not professedly hostile but decidedly critical. There were two reasons for this. On the Continent the mutual hatred of the Calvinists and the Lutherans was almost as great as their common detestation of the Catholics. The point that divided the Protestant churches was the doctrine of the sacrament, Lutherans holding to the cor- poreal Presence more literally than did Calvinists. These disputes were also rife in England, though in a milder form. Then again the German had too little respect for the proprieties and austerities so dear to the Puritan heart. He had expressed approval of amusements like cards and dancing, anathema to the Independents. ...
Though Oliver Cromwell has left no estimate of Luther, there were in his camp a small party of extremists who appealed to the authority of the German to justify their antinomian and anti-social tenets. Such was William Dell, a field-chaplain at Cromwell's headquarters, a preacher in a radical form of justification by faith only. Dell also abused Luther's authority to support an attack on human learning. In his Tryal of Spirits (1660) he printed under the title, Testimony of Martin Luther touching Universities, a part of the Reformer's Answer to Ambrose Catharinus. Dell prefaces it thus: “These now are Luther's own words, which I have made legible to English men. Wherein it is manifest that he condemns Universities in the very Institution and Constitution of them." Of Dell's party was John Eaton, the author of The honey-combe of free justification by Christ alone (1642). In this essay it would seem that he both built upon the Wittenberg theologian and went beyond him.
John Milton confesses that he "had not examined through” Luther's works, and was certainly not deeply indebted to him. Coleridge states that Milton got the idea that Eve ate the apple at noon from the Table Talk translated by Bell. It is possible that the poet may have been thinking of the Reformer in his description of Noah in Paradise Lost:
"The only son of light
In a dark age, against example good,
Against allurement, custom, and a world
Offended. Fearless of reproach and scorn
But this is merely a conjecture. That he thought of Luther, as far as he thought of him at all, is seen in an obiter dictum in the Apology for Smectimnuus, where the poet is excusing the violence of his language. ...
The other chief religious writers of the age have little or nothing to say of Luther.
—Smith, 'English Opinion on Luther'
Note the link on the article's title is far better than the other one, but I left the original one in on the author's name.
I tried finding out on similar lines what Cromwell or his contemporaries thought of John Calvin, but didn't find anything.