The Critical Skills Employment Permit replaces the Green Card type employment permit. It is designed to attract highly skilled people into the labor market and encourage them to take up permanent residence in the state. Here's the Critical Skills Occupations List, where you can check your permit eligibility.
The General Employment Permit allows you to work in occupations where there is a labor shortage in Ireland. You can get the permit to work in any job not on the Ineligible List of Occupations for Employment Permits and subject to the other qualifying criteria.