Quotes from his own pen and from those who knew him best also.  He laboured hard, he fought hard, what mattered to Christ, mattered to Calvin, and he would not take the easy way out of keeping quiet, so as not to offend man at the price of  offending God.  He was not a perfect man, as some of the below displays, none of us are, but he certainly was a great man. And with a spirit to work tirlessly for the Lord,  and so ill almost constantly, unlike Luther, he lost  but all self-awareness, and that is what made him the great servant and labourour he was.  Whether you admire him, or hate him,  this cannot be disputed. You will see how he speaks out boldly against the faults he sees

I received you in a manner but little friendly, for I could not practice hypcrisy, which exists not in my soul. Not only did  the reasons alluded to make me resolute, but still more the horror which I feel at your insincerity.
—Calvin

It was all for the love of truth, and the love of God.

Calvin’s love of truth, his noble, unselfish struggle for the things of God, amid difficulty and danger, so strengthened his soul that it became the abode of a courage unfailing and heroic.With a good conscience, therefore, he could in numerous letters exhort the martyrs of the Reformed faith to remain true unto death. That Calvin was also possessed of physical courage was shown on that Easter day when he withheld the Sacrament from the Libertines at the danger of his life.
Dr Henry

He laboured day and night, when terribly ill, rarely sleeping, yet the Lord preserved his vast faculties of intelligence and logic, despite the toll that not sleeping takes on most people.

I have not time enough to look out of my house at the blessed sun, and if things continue thus I shall forget what sort of an appearance it has. When I have settled my usual business, I have so many letters to write, so many questions to answer, that many a night is spent without sleep.
—Calvin

The whole Church of God mattered to him, and he would never turn his back on someone in need.

I compare myself to a warrior who has slain many enemies, when I have gotten over so many heavy labours. I cannot refuse a man my aid, whatever time and trouble it may cost me.
–Calvin

I do not remember, through this whole year, a single day which was more completely engaged with various occupations. For when the present messenger wished to carry along with him the beginning of my book, there were abou twenty leaves which it required me to revise. In addition, there was the public lecture and I had also to preach; four letters were still to be written; some disputes to settle, and to reply to more than ten interruptions in the meantime; you will therefore excuse if my letter should be both brief and inaccurate.–Calvin in a letter to Farel, from Strasbour, April 20, 1539

Beza wrote of him.

“earnest and dignified as he was, there has rarely been a man whose discourse and friendly bearing were more agreeable than Calvin’s. He bore with wonderful patience the failings of men arising from their natural infirmities, that he might not by, intemperate severity, grieve or offend the conscience of the weak.

Calvin was not a perfect man, he was a frail human being with his own faults just the same as you and I have our faults.
Fisher says of him:

Instead of geniality, which is one of the native qualities of Luther, we find an acerbity, which is felt more easily than described, and which more than anything else has inspired mutltiudes with aversion to him. In his boyhood, he was already  the censor of the faults of his schoolmates, so that he recieved the nicname “Accusative.” Through life he had a tone, in reminding men of their real or supposed deliquencies, which provoked resentment. To those much older than himself, to men like Cramner and Melancthlon, he wrote in this unconsciously cutting style. We learned from Calvin himself that Melanchtlon, mild as he was naturally, was so offended at the style of one of his admonitory epistles that he tore it to pieces. The wretched health, with the enormous burden of labours, had an unfavourable affect upon a temper naturally irritable. He was ocassionally so carried away by gusts of passion that he lost all self control. He acknowledges this fault with utmost frankness; he had tried in vain he says, to “tame the wild beast of his anger.” and on his death-bed he asked pardon from the Senate of Geneva for outbursts of passion while, at the same time, he thanked them for their forebearance.

Otto Scots says of calvin’s personality. 

The personality of this thin, frail, short man was complex, and suffered from the usual lack of comprehension that attends genius. He had a strong will and remarkable energy, but was often ill. Surrounded by lesser minds, he often lost his temper. And he had frightful migraines.
But he was not sour; his gift for making and keeping friends, was extraordinary, Farel, Melanchthlon, Bullinger, Cop Wolmar, Laurant de Normandie, Beza, de Montmorency, Knox, and others, remained close to him through all vicissitudes–and he to them. This speaks volumes.
He was nor perfect. “Painfully sensitive,” to criticism, he could hardly bear any opposition. He had trouble believing that he could be wrong.

Morus wrote of him:

His holy zeal was a righteous one, and it is our drowsiness only which has provided his Christian indignation, his tumultous and story feelings of duty. And what remians for the Christian if he will not use the sword? It is not by soft remedies that he could heal the wounds of zion. He would not have gained his end, and it would have been objected to him, “if you are not yourself convinced in your whole soul, why do you disturbe the existing order of things?”

It seems to me that many of us within the Reformed church today could do with taking a leaf out of Calvin’s book, where serving himself was bottom of the agenda, where he had deep and self sacrificing love for the brethren and the welfare of the church, even if on different continents. Today, sadly, self serving, not doing any more than we have to do, or can do, without looking outright bad to onlookers, but just enough so that onlookers maybe unsure and think we are a people of service when it often wont’ be the case except to our nearest and dearest. The church is suffering and the REformed church has wandred from her roots, precisely because we do not hae the same ethics as Calvin, the same sense of service, and self sacrifice or self denial is quite alien to us often times. Hence the sad decay that triumphed under Calvin’s tutorledge, now has wandered from the course he steered her towards, and you can hardly tell the reformed Christians often times, from any other Christian, apart from their doctrine.
How I lament that fact. And how at times it has added unto my load, because of it. WE are more like Luther, who had an attitude of arrogance and bravado, and full of self import. Now that’s not to detract from the work that Luther accomplished, and achieved, he did far more even with that attitude than is done today, but I feel I would have had a conflict to like Luther as a man or get along with him, where as Calvin was a humble man, despite any or all of the above, and as I think it was B.B Warfield nick named him, he was certainly the theologian of the Holy Spirit.

The above quotes are all citeations from Calvin, Man of the Millennium.