The Gorgoroth Orc Horde is a Mordor battlehost, from the Battlehosts book. One huge block of orcs, which can can as either of shields/bows/two handed weapons, at their choice.
Hithero, I get that you don't like the game, you often state so. However, plenty actually do very much like the game and it turns out that there is more than one type of viable army. Like all wargames, player skill matters a lot and you have to think about the list you are going to take and how it will play. I happily play this game with both its RAW + FAQ (but no Gorgoroth horde!) and also with houserules amongst a smaller group of us, so all their armies have a fairer chance.
That stated - Shadowswarm, the Gorgoroth Orc horde is one of the things that I think break the game a bit too much. It is the worst offender, but I think you can achieve similar things with many horded up Orc/Goblin/Wildmen(?) unit and Nazgul seem pointed out exactly to ally into anything. (apologies, long reasoning follows)
If a player is doing it properly, then there could (and likely will) be three Nazgul in there. GW thought it would be smart to give spellcasters that were already very good value (mastery 3, with two of the three best spell lists) free 'always on' abilities, which buff entire formations. So the bigger the formation, the bigger the payoff. What you have then is a big block of Orcs. Within that block are three mastery three casters with Darkness and Dismay. I would suggest that anyone who wants to abuse things will have Betrayer (rerolls for everyone), Khamul (5+ reflected hits for everyone) and Knight of Umbar (everyone gets highest fight or strength of nearby enemy). That's doable at 1000pts for any list that has integral Nazgul (375pts of heroes), though the horde will not be max-sized - to allow a token common choice. Gobs can manage multiple big blocks though. At 1500pts+ any Evil list can do it.
(the following assumes you know the spell lists) So you want to tackle it? Well, it will probably be right up in your face - Khamul's bubble needs to start early. One of the casters will definitely get WOT off. Now, you need multiple heroes to duel the Nazgul and they need to get into duel range. What if the horde wants to hang back out of melee? It might - each caster has damage spells (SFC, VOW, BD), the unit reflects back damage as instant kills and if they are not facing def (7) troops, then rerolled bowfire seems pretty useful. Def 3 is not a bad thing to be when 1/3 of the hits on you convert to kills on the unit near you, no matter what its strength. I presume any monster is currently staying well-away and the horde player was not able to box in something juicy with the WOT rush and large frontage. So the Nazgul will want to throw some PONs to prevent charges - these can fail and they can be dispelled through Will of Iron, though that is a chancy use of might (I would chance it in this case, though) if these do not suffice, they also have recourse to Transfix, and one of them can make this easier through SS.
Never fear though, because you could easily have multiple units in front of the horde and 375pts of heroes could be something like Aragorn, Faramir and Isildur, so three heroes who are not too concerned about terror and who all have ES, and the might to bump the result further. Hopefully the spell-spam will not delay them too long. I wonder though if that since BD can weaken Nazgul, Nazgul could not themselves be using it to weaken the heroes coming for them? Lets be pollyannaish and not worry about that for now, not worry about the fact that terror rolls can be failed (yes I do regularly fail courage 6 tests) and assume the heroes go in.
Cool. Now the Horde has become fight 10 for every company, very likely 7 extra rerolled attacks per coy. The Nazgul will also all ES. Then the duels will happen.
By my back of the envelope calculations:
You need two hits to kill a Nazgul. 1/3 of the duel table will net you one hit and 1/6 of that table has a 2/3 chance of netting you the two hits that you need. I wish I knew proper math, then I could tell you whether it is better to use might to get more rolls on that table, or reserve it to adjust the table, once you get there.
An ES duel works out like this:
The Nazgul will be completely safe 15/36 of the time. They will also only lose by one (so 1/9th chance of dying from the table, no might involved) an additional 6/36 of the time. So 21/36 of the time they are not at too big of a risk. They really only have to start worrying once the margin gets to about 2+ and/or the hero hitting them has might by that time to ensure rolls become hits.
In my example, the three dueling heroes can all bump that initial duel roll by at least one, say they do: The Nazgul are completely safe 10/36 of the time and lose by 1 a further 5/36 of the time (1/9th chance of then dying, and dueling heroes need more might to improve this). To be really sure of bagging them, you really need to getting several hits on that table, and the variance is quite high. Also, bear in mind that Nazgul actually have a reasonable chance to win ES duels and then get to roll to kill heroes themselves, though resilience 3 heroes are at less of a risk than Nazgul. Now Aragorn in the example is a different matter - he is exceedingly likely to kill a Nazgul when he uses Epic Duel and might, the number of times he gets a bad roll when a Nazgul gets a good one is very small and he has multiple might to convert rolls to kills on the table.
I'd submit, that while you might blithely think dueling out the Wraiths is an answer - you probably have to get three of them (though Khamul is the big target) and most heroes aren't actually that good at taking them them on. You still need to get that margin to generate the kill on the Wraith. The only really reliable ones are the likes of Boromir and Aragorn. The rest will quite likely generate no result.
So on average, the horde sits there and does damage. You really have to keep all tough monsters away. You can damage it with missile fire and Ruin spells. However, if you do, you want to be sure you come out ahead in the model trade, due to Khamul. Once Khamul is gone, then they will likely want to get into melee, with 2HW, the highest fight of any nearby hero (fight 10 if you tried to hit them with ES) and rerolls to hit you. To get Khamul in the first place, you want to get into melee, which is hard to do vs 3 Darkness casters and even when you do, you are cannot be sure of getting even one wraith (let alone the three) unless you have a top-tier dueler.
Of course, you could 'broken' it right back with the old +3 to hit and Epic Rampage combo. The Mumak is also pretty awesome (lets assume you do not in anyway inflict hits on the horde while the Mumak is nearby) since IIRC it does not inflict hits with the movement, just destroys coys. However, darkness spells (stacked SFC, SS & VOW) could do a number on it, assuming the horde can move out of the way / survive long enough. I'd say Mumaks should be able to trample it though.
So - Aside from another particular ability combo (and they have to charge first, with no recourse to MSU, and not go down to BD either), Mumaks and Gondor, games with that horde (or just lots of Gobs in multiple big blocks?) seem very likely to degenerate into an exercise in dice-rolling. The formations seeking to harm the horde are likely to just get attrited away. On average, most of the widely available counters are just not that useful. It doesn't help that while 1-2 Wraiths live, you are pretty much "damned if you do, and damned if you don't" when deciding on how to deal with it.
To finish with an anecdote, a fairly good player had to take that monstrosity on. Beforehand, his line was 'you just have to figure out the right tactics' afterward his reaction was 'that was a bit of a pointless exercise in dice - rolling'
I'm very interested in counterarguments. I couldn't make this shorter without omitting the 'working' (and I've already skipped a bit).