Rule of Two sounds awesome, right up until you spend a couple seconds thinking about it.
One person who decides to ignore it, and the whole thing goes splat.
One accident that either kills the master before he/she takes apprentice, or kills master and apprentice, and it goes splat.
One harebrained scheme that ends up killing them, and the whole thing goes splat.
It's just too fragile to keep going for several millenia, either the teachings start to spread, or it dies out on the first bad accident, or is simply abandoned by those who are supposed to follow it.
It simply strains that suspension of disbelief way past the breaking point for me.
The Sith Empire, in SWTOR or during GHW simply sound cooler, and more realistic to me, they provide structure, constant competition and fresh recruits to replace the dead, and it is not one accident away form destruction.