I've always liked the idea for at the beginning of a series The Doctor messes up BIG time. Something so bad it practically alters the whole future. And for the rest of the series he tries to put the universe back to normal.

So throughout the series you see him encounter the different world that he created.

It may sound a bit naff but i've always liked the idea of this happening.

It is a good concept, but may get a bit repetitive if it was dragged out over a whole series as every story would have to comply to this rule. Still it would work great as a two-parter or a series finale- the threats could get worse and worse and the Doctor must overcome the greatest threat of all to restore the balance- himself!!!!!

I like this idea! With a bit a creative thought it could work, in a Star Trek 'mirror universe' sort of way. He could encounter Daleks is bold bright colours (hang on a minute.........), or a companion who knows him intimately before he even meets them (wait a second..........) or someone could transform from a kindly old gent into someone younger with a taste for blood (what do you mean they did this twice in series 3? i'm sure i'd remember that.....) or perhaps a massive popstar could end up being a lonely servant (okay, now that's just silly.....)!

Isn't the existence of the crack in time and the fact that Amy does not remember the Daleks suggest that The Doctor is in a different dimension. What caused this is mere speculation

I'd love for the doctor to be trying to find something (Kind of like the Key to time) before another time-lord (eg master), or similar. Half way through the season the "villain" kidnaps the companion thus giving them an excuse for companion/doctor lite episodes