Not a villian or a hero.
A dictator yes, but his 'terrible acts of cruelty' aren't exactly comparable to the likes of Hitler and you have to remember these were different times. There were many new freedoms under his rule. For instance 'dissenting' or 'puritan' groups (puritanism was kind of used as a term to lump together all the Protestant groups that didn't conform to the High Church) were allowed to practise freely.
Yes Christmas was banned, but not by Oliver personally - it was done by Parliament and simply enforced during his years as Lord Protector (until 1658).
He also set down the strongest foundations for the British Empire and for the British Army, tied us into stronger alliances with fellow Protestant nations in Europe, and re-admitted the Jews into England in 1656.
What he did in Ireland was indeed terrible but there was some justification for this. The following outlines that viewpoint and can be found here.
On 10 September 1649, a week after arriving at the town's walls,
Cromwell summonsed the Governor of Drogheda to surrender within 24 hours.
His message was clear: no surrender, no quarter. This was fully in accord with
the laws of war. The granting of quarter to those who laid down their arms in the
English Civil War was the exception to the general European rule. Indeed, the
tradition in Ireland was to deny quarter even when it had been promised.
Cromwell cannot be called a war criminal in those circumstances. Immediately
after Drogheda, Cromwell summonsed DundaIk to surrender and, when it did,
kept his troops under tight control.
By the time he reached Wexford, three more towns had surrendered on
terms to himself or his officers. Governor Synott of Wexford knew what to expect.
Cromwell's offer to him was to surrender the town and his weapons, whereupon
the officers would be imprisoned, the common soldiers free to return to their
homes, and the citizens guaranteed freedom from plunder. Or to refuse, and,
under the laws of war, put all life and property at Cromwell's mercy. There is a
dispute about whether the negotiations - which the Governor was spinning out in
the hope that relieving forces might arrive - had formally been broken off when
Cromwell stormed the town. The consequences of the storming were according
to the laws of war then prevailing.
The second line of defence is Cromwell's general restraint. He was in
Ireland for nine months and took 28 towns. He denied quarter and sacked only
Drogheda and Wexford; he offered generous terms elsewhere and honoured
them to the letter whenever they were accepted. Most remarkable was his
restraint at ClonmeI. He lost more than 2,000 men in a foiled assault there. He
then took the town on terms and honoured them, although perhaps 200
retreating soldiers were chased and killed.
Thirdly, when he wrote that the sack of Drogheda would 'tend to prevent
the effusion of blood for the future', he meant it. It may be that Drogheda and
Wexford were his Hiroshima and Nagasaki: the application of an economy of evil
to save more lives in the long run. In the 17th century, as in the 20th century, that
is a morally contested view. But it has not led to trials for war crimes. The
intention was honourable.
Fourthly, the evidence for civilian deaths is far less clear than the evidence
of the killing in cold blood of disarmed and surrendered combatants. There is
only circumstantial and hearsay evidence that civilians - other than clergy - were
killed in cold blood. To convict Cromwell of war crimes requires evidence of civilians
killed in cold blood.
Fifthly, there is a tendency to blame Cromwell for all the horrors in Ireland
in the 1650s. There were certainly atrocities after his departure. General
Fleetwood introduced a policy of reprisals which pre-echoes Nazi cruelty. If an
English soldier was killed by snipers or Tories (bandits), then the nearest
community was given 24 or 48 hours to hand over those responsible for
summary execution, or they were all seized and transported into slavery. The
whole English political and military establishment in Ireland can be blamed for
this. But Cromwell cannot. There is no evidence he approved of the policies and
plenty of evidence that he sent his son, Henry Cromwell, to govern Ireland in
order to mitigate their severity.
Furthermore, he worked to ameliorate the effects of the Land Settlement,
abandoning the policy of mass transportation. While Protector, no one was
executed under the Act of Settlement, and the policy of enforced movement to
the west was largely abandoned. There is a case for saying that when Cromwell
was Lord Protector, he treated former Irish royalists and Confederates much as
he treated former English royalists and Catholics. But since there were proportionately
far more of them in Ireland, their continued suffering is more evident."