Tennant resignation

I heard yesterday that David Tennant has resigned as Doctor Who. This decision leaves me with divided feelings - on the one hand, having a Doctor prepared to stay the course for so long is unusual and welcome; on the other hand, regeneration and the associated change in personality (and appearance) is central to the whole Doctor Who thing (even though it was only invented to keep the series going after William Hartnell) - by staying in one persona for so long this aspect of the Doctor as an alien is lost. Do we as viewers build a relationship with the actor, or with the Doctor? The divided feeling suggests that the answer is probably both.

Also fair to point out that in the first year of the revived series, the Doctor was Christopher Ecclestone. I enjoyed series one immensely and remember the disappointment at hearing that Ecclestone was leaving and that "Casanova" was to replace him... in fact, the regeneration was part of what gave series one it's dramatic structure and climactic ending.

But I want to end this post firstly with the point that with the 2009 special episodes with Tennant still to come, I'm actually talking about an event two years ahead as if it has just happened - how apt. Secondly, I'm just reflecting on how much I've enjoyed from the Tennant years - for instance right now I'm thinking of the thinly veiled references to Douglas
Adams (the dressing gown in the Christmas special, the 42 episode, the Starship Titanic episode...)