Right, The Big Bang Theory consists of five really good season of Television Comedy. It started out about a set of "geeks and nerds" who struggle to fit in with the conventional way of life, resulting in the group being placed in outstandingly funny social situations and because of this the first 2/3 seasons of this show are extremely good, the characters and the writing for the characters is world class. However where this show really excelled was in the acting ability of its lea,. Jim Parsons' portrayal of Sheldon Cooper is nothing short of outstanding, possibly one of the greatest performances in a Sitcom ever.
Why did I only mention the first 2/3 seasons as being this good? well the truth is the show does decline ever so slightly in the later seasons. This is due to a few different reasons, namely the addition of characters like Amy, Bernadette, Priya and a subsequent shift in focus from Science, Sci Fi and Comic Books to the social development of the main characters. I must maintain that although the show does decline it is still very very VERY good. The show needed the change in direction to keep it fresh and up to date and I think it works, I know some people will inevitably disagree (while I write this no other reviews have been posted)
Through all of the changes the one extraordinary constant is the exceptional acting of Parsons, which ensures that the show is top drawer and well worth buying and watching over and over again.