As an amendment to the above, most British historians would disagree that
Charles I was solely or even mostly to blame. The events leading up to the outbreak of the
Civil War were too complex to be able to label one side as the guilty party. Charles was wrong to try and govern without
Parliament but at the time, many people believed in
divine right so he cannot be blamed too heavily for being
arrogant. Curiously enough, his real mistake was trying to be a "good"
Protestant prince by waging a war against the
Catholic continental countries. Had he not fought with
Spain, he would have not needed the "Ship money". Although this tax did irritate many people, it did not turn Englishmen against him. The period where he ruled without Parliament was relatively
stable. It was only when he idiotically tried to force the
Scottish Church to adhere to his new religious plans that things came to a head. He needed Parliament to raise money and an army to combat the Scots. Parliament would do so but they wanted something in return.
Parliament was partly to blame over the outbreak of war due to the plot of some MPs to have the Earl of Strafford killed. They falsely accused him of treason by manipulating what he said in a private discussion, overheard by someone. In the end Charles was reluctant to order his execution but felt that he had to. Parliament also brought the country close to conflict by their rather bigoted opinion of themselves. They did represent a wider electorate but only a minority of richer people. There was no form of democracy like today. Also the king had the moral as well as legal right to do as he pleased. Though there were many MPs who believed in having more people eligible to vote, the majority of MPs were simply in a plot to increase their own power.
On the war as a whole, the country did not side against Charles. There was a relatively even split in terms of who supported who. Families more often split over this matter than they agreed in supporting one side. Even a significant number of MPs sided with Charles. As a whole, the commoners and other ordinary people sided with neither the Cavaliers nor the Roundheads. There is a famous example of this. In a house, there would be a large chest pushed up against a wall. On one side there was an inscription saying "God save the King" and on the other "God save Parliament". Depending on which side came into the house, the chest would be quickly turned to face the appropriate side. Charles lost because of Parliament's New model army rather than because a majority of people sided against him.
After the war, Charles was brought to trial. Of course this is one of the most ridiculous things of all. Technically, there is no way the monarch can be brought to trial, especially for treason. In Britain, treason is normally committed against the Crown. Even today, no one can be sure whether the procedure was legal. More importantly, even after all the suffering caused by the war, most people did not want Charles killed. There is also the strong possibility that a large part (not necessarily a majority) of the judges were pressed to sign the death warrant. Throughout time, English judges have acted on the law and precedent. Why they should therefore have broken with tradition so easily begs questioning.
In the aftermath, Cromwell set up his own dictatorship. He actually had more absolute power than Charles because he had kicked out a majority of Parliament's MPs. In the end those left rubber-stamped all of his decisions. He wisely ended the war against Spain and increased the prosperity of the nation. However this was outweighed by his religious extremism. In a time where religion really mattered to people, this was rather cruel. Only a minority of Englishmen were Puritan but the majority were forced to adhere to not only their religious scripture but also a lifestyle devoid of pleasure and fun. Drinking, singing and acting were widely banned. You could even be punished for celebrating Christmas in the wrong way. Worst was what he did to the Catholics in Ireland. No quarter was given and they were massacred wherever Cromwell's soldiers went. This is the root of the current problems in Northern Ireland.
When Charles II came back to England, it was to the salute of a Parliamentary general, Lord Fairfax, and the behest of Parliament, rather than at the head of an army. Cromwell had appointed his son his successor. He was given the name "Tumbledown Dick" because he was so disinterested and useless at running the nation. Charles II was a good king. He did his best not to have Parliamentarians hounded by Royalists seeking revenge. He brought stability to the land, also bringing relative happiness by ending the repressive policies of Cromwell in the entertainment sphere. After the suffering and then boredom of the years before, he felt it was important for the nation to have fun again. He also recognised that Parliament needed to have more power, though the monarch remained effective head of the country for many years to come. Finally, the nation was able to settle down.