Questions about the gameplay of Heroes 6.

I read that the "Charm" ability of the Lilim can stop or disable an enemy unit for 1 turn. What about 2 turns? And how effective is it?... Does it work on everyone?... Who is it ineffective against?

It's effective, especially if you deploy 2 units, as they are ranged attackers. It lasts for 1-2 turns. If you attack, the effect will dissipate.
It doesn't work on undead. And it's also ineffective against some units in other factions.