For saying Charles I is successful you could probably talked about how he was able to restore monarchy successful until today and brought back the type of 'settlement' that Cromwell was looking to achieve with his protectorate. With England being used to the monarchy as well as the other Kingdoms Ireland and Scotland, he was able to get this underdone with fairly any opposition as parliament became united on this idea. There was a parliament called/in session every year from 1660 to 1679 and it is said that Charles I had the most power of any Stuart king at that point from 1681 to 1685 especially when he called no parliaments and was ruling with french money. You could say he is also successful because he defeated the exclusion crisis, which paved the way for next in the line, although James was Catholic, to become monarch. In comparison to Cromwell's succession of the protectorate to his some Richard he wasn't able to stay in power for a long period or use his power whatsoever. Looking at his restoration itself, you could talk about the land settlements and declaration of breda assuring the New Model Army would be paid and that they won't be prosecuted for Charles I's execution (only those directly involved) as only 30 people were prosecuted by the Indemnity Act. With the Army getting what they wanted: pardon and pay, they disbanded and this eliminated a force that huge military and political impact from the 1645 onwards till this point in time (early 1660s). There are some other things you could talk about too but this is what I thought of from the top of my head now haven't looked at stuarts since the exams last month.