What Are The Advantages Or Disadvantages Of A Parliamentary Form Of Government?

Generally a parliamentary form of Government is a democratically elected form of Government (although there are exceptions to this, for example, once Hitler had been elected to power in Germany he retained the Reichstag, but effectively barred free elections).  
Democratically elected Governments can be viewed as being representative of the people and therefore less likely to be extreme in nature or to exact cruelty on their electorate.  In short they will protect and attempt to enhance the quality of life for those who voted them in.
However, there can be disadvantages as well.  Democratically elected Governments may be unwilling to address some of the trickier questions or harder issues, for fear that if they raise taxes too high or cause major inconvenience to some of the electorate, they will not be voted in again.
Thus parliamentary forms of Government may be viewed as flawed, but perhaps they are a safer option than a dictator or supreme ruler.