This is the best TV show ever and this season doesn't disappoint. The end was obviously changed (from Kripke's original vision) for the purposes of a season 6 but it is still fantastic. The writing is wonderful, how they mix the intensity of what's going on week after week with fantastic one liners and the emotion in the relationships between the characters is fantastic. The acting is also second to none (Jared, has his 'overacty' moment when Sam's 'doing his thing' but imagine how you'd feel for hours on end holding your hand up to nothing!! He comes into his own and shows some real talent towards the end of this season) and the subtle expressions (mainly of Dean/Jensen) and silent exchanges between characters is fabulous. The addition of Castiel in season 4 came against harsh criticism by some but I think he's a wonderful addition to a long running series and takes some of the pressure off the brothers - stopping it becoming entirely about them all of the time.
Just brilliant. I don't like telling people good things about it because I want to keep it culty but I have to defend my favourite show ever against any naysayers.