This was a mini episode that got buried away on the BBC Red Button at first but Doctor Who fans will know its true importance and worth as it is the episode where we finally see what became of the 8th Doctor, who we met all too briefly in the 1996 TV Movie.
It acts as a good episode in itself, but also as a very important link between the series as a whole. It sounds odd, but we as an audience do need to see the regeneration of a Doctor, however painful that change can be (I'm happy to see Capaldi's regeneration now though - I've not enjoyed his time in the TARDIS). This mini episode gives us the closure we needed with the 8th Doctor.
It acts as a good episode in itself, but also as a very important link between the series as a whole. It sounds odd, but we as an audience do need to see the regeneration of a Doctor, however painful that change can be (I'm happy to see Capaldi's regeneration now though - I've not enjoyed his time in the TARDIS). This mini episode gives us the closure we needed with the 8th Doctor.