The variation of characters within this programme makes it an interesting watch and often allows it a great deal more scope than other shows. Overall narrative cohesion can suffer slightly because of the construction but sustains a good standard most of the time.
The show is usually very well written and the actors do good turns when given the opportunity. It also has a very good style and pace that give the whole series a nice character.
I recommend approaching this on an episode by episode basis and the variation can mean you'll love one episode and hate another. Be patient and you'll find good things here.