The way the new series is written, there is a lot of build-up, and jumping right into the middle will cause problems. For instance, the third episode of Season 3 (before the middle) gives you a hint about the Season 3 finale. You will miss Rose, not know the deal with Captain Jack Harkness… basically you really should start with Chris Eccleston’s first episode or you will miss quite a bit.
@JilltheTooth Not really. There is a lot of stuff in the new series that doesn’t make total sense if you don’t know the first two decades of the series. Stuff like Daleks, The Master, Sarah Jane Smith, regeneration, etcetera; stuff that is kind of glossed over in the new series. You don’t need to watch the first 26 seasons, but understanding the new series is much easier for those of us who grew up during the Tom Baker years.