Re: How to play as mordor
use the Nazguls
Their command stats, dread stats and their fear-related special abilities make them great to rout enemy armies. No army without a general inside can withstand them, they will flee in mass in front of them, especially the WK; if they have general, your first goal, when possible, should be to kill him and then use fear special abilities (coupled with flanking for the best effect) to rout them.
they will be the only cavalry units you'll have and for the first part of the campaign they will also be the only effective flanking unit (until you get trolls), they already have traits/ancillaries which give them extra Hps; they have not great charging bonuses, but very good attack and excellent defence, which means they work very good in charging and can handle quite everything in melee, only avoid heavy lancers, halberdiers, pikemen and other similar units.
with MOS, Mordor is a walk in the park, as you will have 9 nazguls, to be split in two armies (I usually use 4 in one army, 4 in another and leave Kamhul to take care of Mordor northern regions); give them cannon fodders (I usually pack up as much archers as I can, they serve perfectly in this purpose and plus can shot some arrows) and when you can add some better unit (morannon guards, dismounted numenoreans) use them as back up to fill the gaps in your battle line or to face/flank the best enemy units. Trolls and later Ologs will become your extra flanking units, when you'll have enough of them you can divide again your Nazguls (2+2+2+2) and give them 2-4 units of them each army.
by using this tecnique you'll have two effective armies since the beginning, and you can keep the pressure on Gondor without need to stop, as long as you will keep sending meatshield troops (that you can recruit quite everywhere)
truly, Nazgul are powerful, if you learn how to use them properly and exploit their special abilities, you won't even need to wait for trolls to steamroll ME 
F