I really like the idea of this class. I've always liked the idea of power based on balance of two opposites.
Anywho, my 2 cents is this:
Neither Good Nor Evil: A Master of Life and Death is not restricted by alignment in the same way a cleric is: a Master of Life and Death may cast all spells from the cleric list, including Chaos, Good, Evil, or Law.
With the flavor of the class, and the title of the ability even, I'd say they should be restricted to either good or evil spells. Chaos and Law should still be affected depending on their alignment.
However, if you'd like to keep that clause, I might suggest that you rework the alignment requirement. Maybe put it at True Neutral?
As it is, I don't think a neutral evil or neutral good person would fit well in this class anyways... idk, maybe they would. But it seems more like the CN, N, or LN type class.
That's just me though.


Also flavorwise, the truth and language abilities really don't seem to fit. Perhaps you could take those out and/or replace them to help with the power level a wee bit? I know it wouldn't be much... those are hardly the most powerful...


As for the last ability, might I propose an interesting fix that keeps it the same way, but also hurts it a little and makes it less uber awesome? (though it still really really rocks. It's above immunity to negative energy).

Perhaps negative and positive energy spells not only both heal the person, but they both only half affect them too. Reduce all negative/positive energy by half.