well it was pretty much a military dictatorship for most of the period the Commonwealth lasted .
That's what tends to happen with revolutions; one form of tyranny is replaced with another, the last often worse than the first.
Still, beheading the odd monarch, oligarch etc every now and then, keeps the bastards on their toes. France in 1789 and Russia in 1917 did the rest of Europe a favour imo, even if it didn't go so well for them after that.

