Dirk Gently started out life in the books of the late Douglas Adams. The books are fantastic, they will keep you laughing and entertained until the end.
The TV series however will not, it’s just total bollocks in my opinion, I bet Douglas Adams is howling in his grave at how bad each episode was, they were only vaguely related to the Dirk Gently books by the names of the characters. The story lines were a confusing mishmash of crap and most of the original jokes and quirkiness of the characters was lost.
I give the TV series 2 carrots out of 10, and that is being generous.
To learn more about the Dirk Gently books have a look to the Wikipedia page.
To learn more about the TV series have a look to this Wikipedia page and the BBC website.
You can see the trailer for the original pilot episode of the series below: