As we all know, our beloved show took a very different approach when the lead actor decided to bow out. Rather than writing the character out, they simply replaced the actor - and included a narrative device that explains exactly why he looked completely different.

The concept of regeneration has undoubtedly changed over time. The original description of the process from 1966 (when it was referred to as "renewal") from the production team was thus:

The metaphysical change which takes place every 500 or so years is a horrifying experience — an experience in which he re-lives some of the most unendurable moments of his long life, including the galactic war [which was believed, at this time, to have been the cause of the Doctor and Susan's departure from their home planet]. It is as if he has had the LSD drug and instead of experiencing the kicks, he has the hell and dank horror which can be its effect.
Clearly, the concept has evolved significantly now - it's not every 500 years, it's whenever he would die. But the idea of him re-living some of the most unendurable moments of his life has survived on occasion - I'm particularly thinking of the various enemies appearing in the Doctor's mind when the Fourth Doctor was hanging from the satellite dish, or the Master appearing to the Fifth Doctor.

So, let us know your thoughts on the whole regeneration thing - particularly with reference to Season 4. Did it give the show a new lease of life?