Hugh Laurie is the irascible Dr Greg House, head of Diagnostic Medicine which means they give him all the really difficult cases to solve - it's like the A Team, if no-one else can help you, and if you can find him, maybe you can call Dr. Greg. House.
He is ably assisted by his three junior docs and has had a an on-off thing with the female one. (Plus I reckon a bit of chemistry with the head of the hospital). He is a drug addict after he suffered a sort of stroke in one leg, I can't remember the details about this but it was shown in flashback in the last episode of the first series, where his ex-gf reappeared with her new husband. She is the only person he has ever let into his heart and he has never recovered.
Also, Robert Sean Leonard is in it, out of Dead Poets Society. He is House's best mate, and (bizarrely) rarely has scenes with anyone other than Hugh Laurie. He is an oncologist.