In a parliamentary system, there is an executive branch of government which is depended on the direct and indirect support of the parliament. The support is given through a vote of confidence. The Parliamentary system has an apparent differentiation between the head of government and the head of state, with the head of government being the prime minister or premier, and the head of state being a monarch or an elected president. The president or the monarch is the first citizen and has the highest authority but the "executive power" needed to run the nation vests with the prime minister along with his cabinet of ministers. It is easy to pass legislation in the parliamentary form of governance. It is quite ideal for nations that have diverse races, religions, ethics and ideologies. The criticism faced by parliamentary government is that there is too much power vested with the executive (read the prime minister and his cabinet), which leaves the legislature and judiciary with little scope for governance.
In the presidential form of government, all executive power lies with the president. His executive power is separate from the legislature to whom he is not accountable. The advantage of the presidential form of governance is direct mandate (president is directly elected by the people), separation of powers, faster decision making and stability (the presidents sticks to his tenure unlike the prime minister who can be toppled at any time). Critics believe that the presidential system of governance is not constitutionally stable. Further the hindrance in removing the president before his tenure can be a problem especially if the governance is a failure. Thirdly, if the legislature and presidency is kept separate, there is lack of accountability and both the parties tend to get loggerheads at each other.
In the presidential form of government, all executive power lies with the president. His executive power is separate from the legislature to whom he is not accountable. The advantage of the presidential form of governance is direct mandate (president is directly elected by the people), separation of powers, faster decision making and stability (the presidents sticks to his tenure unlike the prime minister who can be toppled at any time). Critics believe that the presidential system of governance is not constitutionally stable. Further the hindrance in removing the president before his tenure can be a problem especially if the governance is a failure. Thirdly, if the legislature and presidency is kept separate, there is lack of accountability and both the parties tend to get loggerheads at each other.