Although Cromwell did not set out to make this happen, he ended up creating a dictatorship with himself as the head of the government. So you can say that the type of government he created was a dicatatorship.
What Cromwell really wanted, and what he first tried to set up, was a republic run by Parliament. However, for various reasons, this did not work out very well. Cromwell came to believe that he needed to take more and more control of the government. Eventually, what was left of Parliament after Cromwell got rid of his political enemies dissolved itself and gave all its powers to Cromwell. Cromwell also set up a system in which eleven of his generals ran the local governments around the country.
By doing these things, Cromwell set up what can best be described as a dictatorship.