1649 to 1660, and yes, it was wrong. There are few historical figures I despise with the passion I despise Oliver Cromwell. This issue was exhaustively debated on FR before I joined. See this old thread:
Catholics to snub Cromwell festivities
What about the overthrowing of the Tsar?
Yes, I'm against that too. Nicholas II was a good man who loved his country. The abolition of the monarchy paved the way for the evil Soviet tyranny which was arguably the worst government in history.
The Hohenzollern dynasty in Prussia was barely a century old (previously they were just elctors)
Huh? The Kingdom of Prussia was established in 1701, 217 years before the monarchy was overthrown. In any case, I don't see what your point is.
The Scandanavian royalty is a farce as is the Belgian and Dutch.
How are they a "farce"? They provide a patriotic rallying point for their people, have devoted their lives to public service and charity, lend crucial glamor to the Nobel Prize cermonies, and embody their nations' heritage and traditions.