A further thought on 'Waters of Mars'...
Under the cut to save those who've not yet seen it...
Ten's been heading this way since 'The Christmas Invasion' - the only wonder is that Power!Mad!Ten didn't emerge sooner. He told Jack, back in 'Utopia', that taking the power of the Time Vortex into himself would make a Time Lord into a vengeful god, and Ten's teetered back and forth on the cusp of that regularly (The Christmas Invasion - see Ten's reaction to Harriet Jones giving the order to blow up the Sycorax ship, School Reunion - see Ten's reaction to Mr Finch's offer, Human Nature/The Family of Blood - see Ten's punishments of the Family, etc.). Basically, saving Rose's life made the Doctor insane - he's just been hiding it reasonably well for the most part...
Ten's been heading this way since 'The Christmas Invasion' - the only wonder is that Power!Mad!Ten didn't emerge sooner. He told Jack, back in 'Utopia', that taking the power of the Time Vortex into himself would make a Time Lord into a vengeful god, and Ten's teetered back and forth on the cusp of that regularly (The Christmas Invasion - see Ten's reaction to Harriet Jones giving the order to blow up the Sycorax ship, School Reunion - see Ten's reaction to Mr Finch's offer, Human Nature/The Family of Blood - see Ten's punishments of the Family, etc.). Basically, saving Rose's life made the Doctor insane - he's just been hiding it reasonably well for the most part...