This is the type of show that you watch to get a good laugh and relax and to bother yourself with difficult plot to understand. As mentioned before, first three seasons are perfect, the last one... not at all... it doesn't even follow up the previous events and all of the characters that you get to love just dissapeared and were replaced by new ones, who are just boring compared to the ones before...
Nevertheless, except the 4th season, this series is great :)