Were the military brutalities inflicted by Cromwell on Ireland much worse than most medieval warfare during this time period?

The measurement of human brutality against itself is not mine to comment on. I confess the suggestive framing of your question gives me pause: Whether they were killed only in proportional depravity was likely small comfort to the dead. However you may find the writing of Cromwell himself illustrative of his intent. In a letter to the Speaker of the House William Lenthall, several days after the siege of Drogheda, Cromwell justifies the massacre thusly:

I am persuaded that this is a righteous judgment of God upon these barbarous wretches, who have imbrued their hands in so much innocent blood; and that it will tend to prevent the effusion of blood for the future. Which are the satisfactory grounds to such actions, which otherwise cannot but work remorse and regret.

Cromwell later writes of the civilian death toll at Wexford:

I believe scarce one in twenty can challenge any property in their houses. Most of them are run away, and many of them killed in this service. And it were to be wished, that an honest people would come and plant here; - where are very good houses...

Writing on the aftermath of the conquest, William Petty—Cromwell's physician-general, noted:

It follows also, that about 504 000 of the Irish perished, and were wasted by the Sword, Plague, Famine, Hardship and Banishment, between the 23 of October 1641 and the same day 1652.^1

Draw from that what conclusions you will. Others here are no doubt better qualified to respond in detail.

Peripherally for my own sake, there is quite a tradition regarding Cromwell in folklore. While hardly historical testimony, without question the perception was of Cromwell as not only an extraordinarily cruel man, but in some sense a living personification of evil. As Seán Ó Súillebháin writes in The Folklore of Ireland:

The hatred which Cromwell's ruthless deeds in Ireland in 1649-50 aroused in the hearts of the Irish people is reflected in...tales from the oral tradition.^2

One such tale, if you'll forgive the long transcription, comes from County Galway in 1935:

There was a man here in Ireland long ago. He was a gentleman by the name of O'Donnell and he was very friendly with a monk in the district. One day the monk told him that there was a great change to come over Ireland; that England would take over Ireland, and that a leader of the name of Cromwell would be throwing the Irish people, who had land, out on the road and would be settling his own people from England in their place.

'The best plan for you,' said the monk to O'Donnell, 'is to go off over to England. The man they call Cromwell is a cobbler. You must travel around England, with a notebook, and ask every man you meet to sign his name in the book, promising that he won't ever take your land or dwelling-place off you. Keep on travelling like that until you go to where Cromwell is living.'

That was that! O'Donnell crossed over to England and he was travelling around with his book, pretending to be a bit simple, asking everyone he met to sign his book that he would never take his land or dwelling-place off him. He kept going till he came to Cromwell's house. He went in and asked Cromwell to put a side-patch on one of his shoes. When the job was done, he handed a guinea to Cromwell.

'A thousand thanks to you! That's a good payment,' said Cromwell.

'Now,' said O'Donnell, 'I hope that you will sign this book that you will never take my land or dwelling-place off me.'

'Why wouldn't I promise you that?' said Cromwell.

He took hold of the book and signed in it that he would never take his land or dwelling-place off O'Donnell in Ireland. When he had done that, O'Donnell went back to Ireland.

Some years later, there was a great change in England. Cromwell rose up high and took the power from the king. then he came to Ireland. He was throwing the people out of their land, whether they were noble or lowly, and killing them. He arrived at O'Donnell's house and struck a blow on the door.

'Out with you from here!' he shouted. 'You're here long enough!'

'I hope you won't put me out until you and myself have dinner together,' said O'Donnell.

'What sort of dinner have you?' asked Cromwell.

'Roast duck,' said O'Donnell.

'That's very good,' said Cromwell. 'I like that.'

Cromwell went into the house and two of them started eating the dinner. When they had it eaten, O'Donnell took out his book and showed it to Cromwell.

'Do you recognise that writing?' said O'Donnell.

'I do, 'tis mine,' said Cromwell. 'How did you know that I'd be coming to Ireland or that I'd rise so high?'

It was no use for O'Donnell to hide it; he had to tell the truth to Cromwell.

'There was a holy monk in this place,' said he, 'and it was he that told me that a great change would come in Ireland and that it was a cobbler in England by the name of Cromwell who would come here and put me out of my land.'

'You must send for that holy monk for me,' said Cromwell, 'and if he doesn't come, I'll cut the head off him!'

O'Donnell went off and found the monk and brought him back to Cromwell.

'How did you get this knowledge?' asked Cromwell.

'I got it from Heaven,' replied the monk.

'Now you must tell me how long I will live,' said Cromwell.

'You will live as long as you wish to,' said the holy monk.

'I'll live for ever then!' said Cromwell.

There was another big gentleman from England along with Cromwell.

'And how long will I live? Will I get a long life?' he asked.

'If you pass the door of the next forge you meet on the road alive,' said the monk, 'you'll live a long time.'

'Ah, I'll live for ever so!' said the gentleman.

That was that! Cromwell didn't evict O'Donnell; he left him where he was, and went away. Himself and the English gentleman and their troop of soldiers went along, and when they were passing by a forge, Cromwell said:

'There's a shoe loose on one of our horses. But luckily we're near this forge!'

He jumped off of his horse and entered the forge. The smith was inside.

'Hurry up and put a shoe on this horse for us!' said Cromwell.

The poor smith was trembling with terror. He hurried here and there about the forge, looking fo a good piece of iron. He was afraid that he wouldn't be able to get a piece good enough for Cromwell and his army. Cromwell himself was searching around also, and he spied an old gun-barrel stuck above one of the rafters of the forge.

'Here's a piece of iron that's good!' said he.

He pulled down the old gun and shoved the barrel of it into the fire—he was well used to working in forges too, for his father was a smith. He started to blow the bellows. The English gentleman was standing outside the door. It wasn't long till the shot went off through the mouth of the gun and it struck the gentleman on his vest pocket and went through his body at the other side. It killed him. Cromwell ran out when he heard the noise outside, jumped up on his horse, dug the spurs into it and raced for Dublin. As he was galloping along the road, whom did he see, walking ahead of him, but the holy monk! When the monk saw Cromwell coming towards him, he tried to run down and hide himself under the arch of a bridge.

'Come up out of that, you devil!' shouted Cromwell. 'If I have to down to you, I'll cut the head off you!'

The monk came up to him.

'Tisn't from you I was hiding at all,' said the monk, 'but from the man behind you.'

'What man is behind me?' asked Cromwell.

'He's sitting behind you on the horse,' said the monk.

Cromwell looked behind him and he saw the Devil at his back. All he did was dig his spurs into his horse and race for Dublin. He went back to England and never returned to Ireland again. After spending a while in England, he grew restless. The King of Spain died, and his son, who hadn't much sense or knowledge about ruling a country, took his place. Cromwell decided on a plan which seemed very good to him. He wrote a letter to the young Spanish king, inviting him to England and offered him his daughter in marriage. When the king got the letter, he sent for his advisers and told them about it.

'That's a plan of Cromwell's,' said they, 'to try to get into this country and take over the kingdom. Write a letter back to him and say that you'd like such a marriage arrangement, but you want a year to think the matter over; when the year is out, you might like the offer very much. You must be strengthening your army during the year, and at the end of it, write to him and say you don't wish to marry the Devil's daughter!'

Cromwell happened to be shaving himself when he got the letter at the end of the year. He had one side of his face shaved, when the letter was handed to him. When he read the piece about the Devil's daughter, he cut his throat with the razor and fell dead.

About the time when Cromwell killed himself, a ship was entering Liverpool, and the captain saw, coming towards him in the air, a fiery coach drawn by dogs, and they crying out: 'Clear the way for Oliver Cromwell!'^3

In this illustration of the story one can see how Cromwell is imagined—dread accomplice riding pillion.

I've also transcribed a further Cromwell tale below.

^(1 • Sir William Petty. The Economic Writings of Sir William Petty. Cambridge, England: Cambridge University Press, 1899. Digital.) ^+

^(2 • Seán Ó Súillebháin. The Folklore of Ireland. New York, United States: Hastings House, 1974. p. 132.)

^(3 • IFC MS 157: 176-183. Recorded on Ediphone in August 1935, by Liam Mac Coisdeala, full-time collector, from Marcus Ó Neachtain, Ard Mór, Carna, County Galway.)