Southern Gate, Pelennor Fields, Black Gate by Healey
The Lord of the Rings: The Return of the King on SuperCheats.com
This is a Lord of the Rings Walkthrough for only three levels which plenty of gamers have trouble on as far as problem solving is concerned: the South Gate, the Pelennor Fields and the Crack of Doom. 

The South Gate
This is a great level to get experience nice and quick. After a few things happen, everything degenerates into a melee with your character wading through Orc bodies up to their kneesÖsounds fun.

First off, just run forward towards the gate. Before you get to it, however, a big troll will shut the gates and jump down to play. As he does, orcs will pour out of the river and the surroundings to heavily outnumber your fellowship. Ah well, thatís how the Fellowship likes to fight, isnít it? Outnumbered but never outgunnedÖ
Quickly run back and to your left there is a spear that is best to ram up that trolls backside. Do it quickly before any orcs can come and knock it out of your hands. If you donít kill him, he will come back to haunt you, but he wont move from where he is. Remember, youíve got to go through that gate sometime.
Time to play! Hack your way through the orcs while travelling to the left and slightly back. There are two catapults there. When you set them both off it will send a tower over to the right crashing down, providing a way up to the top of the gate. The problem is getting over there.
If this is your first time, just keep pressing A through the crowds. Anything slower and those orcs will be all too willing to pull your arms off. Donít worry, none of them have shields. 
If this isnít your first time, just keep pressing A! Lightning Strike is a great combo, but Swift Justice is easily the best. 
Make your way over to the tower on the right. If you want you can set off the last catapult which is slightly back, and it will hurt the troll at the top. But not much, so if you are low on health its not worth it.
Run across the bridge given by the rubble and climb the ladder. There are three Uruk-Hai up here, and you will probably be on low health by now. Just donít do anything stupid. Start climbing up the steps, but donít go right to the top. There is just a low wall separating you from a big angry troll who will eat your babies. Staying just below the top of the steps also stops any marauding orcs hacking your legs off while you pelt the troll with arrows (always safe) until he looks like a hedgehog on steroids. 
A few seconds later, an Olliphaunt arrives. The cutscene will probably end with you standing at the edge the wall surrounded with orcs and a hail of arrows coming your way. So while the cutscene is running, just keep pressing B. you can block arrows, donít forget. The Olliphaunt will fire two volleys before having a rest, and so use that first time to dispatch the orcs around you. If you have time, kick the ladder down in front of you by going up to it and pressing X. now just hold L and riddle the Olliphaunt with arrows. You can keep hold of L and still press B so there is little need for endless thumb twiddling on this. 
After it explodes (I always wonder how oversized-elephants can explode), you will be able to open the gate. If you didnít kill the troll down below then he will hold the gate shut if you try to open it. As well as that, more orcs will begin to jump out of the tower to the far left of the wall to make your life difficult. Use the two pots of boiling oil to the right of the wheel to burn the troll if you didnít kill it, and open the door. I think it only takes three turns. In between turns, knock back any orcs who are harassing you, but donít waste time by finishing them off or the gate will just close again. 
Once it is open, eight orcs will run out, but they donít really pose a challenge. Just fight your way back to the gate and massacre them. It might be an idea fire any remaining arrows you have left blindly for a couple more kills, then run through the gate. Level done!

Pelennor Fields

This level starts off with mass slaughter. Yay! 
This level is easiest with Legolas, especially if he has Elven Bow Mastery. But it is quite completeable with anyone. 
Start off by getting stuck in! kill 60 orcs or Easterlings and youíre set for the first part. The Easterlings (warriors in gold and red) are made of sterner stuff than orcs, and will keep coming even if you can smack them to the ground more than once. Final Judgement is the best combo to use on them, but make sure that there is nobody around to stop you completing the combo or I will come around and break your arm! 
I warn you now, the Easterlings with shields are right little buggers! You often get mobbed and canít get a decent heavy swing in without some orc jabbing a sword in your ribs! And the Easterling captains are even worse! Try and get them alone, and you can take them down. If they start running at you, start blocking or they will knock you to the ground which is really frustrating. Break their armour with a fierce attack then proceed to dice them to pieces. 
When 60 of the Mordor scum are dead, the Mumakil will start making a beeline for Merry and Eowyn. You will automatically run up to a plateau to the right of where you started. With decent arrows, it takes two arrows to break each piece of the Mumakil armour and two more to blow it up. But if Legolas has Elven Bow Mastery and Mithril Arrows, he can stop it in two shots! If you need them, there are ballistas (which reload) and a few spears lying around. Problem solved.  
Another one will start making its way towards the two suckers at the end of the valley, and you canít hit him from where you currently are. You have to quickly run down the slope leading from the plateau, run across the valley floor and up the other side which is directly opposite. The incoming enemies will more or less ignore you, so donít give them any reason not to. 
Run up the other side and to the right to where the Mumakil is on his way. There will be two Easterlings or Orcs up here, so kill them before turning on the Olliphaunt. 
When he is dead, the Witch King will join the party, swooping down and taking out Merry and Eowyn. When you start again, quickly run to the left side of the plateau and pelt him with arrows before he kills them. There will be an Easterling dawdling his way up the side, but ignore him for as long as possible (donít matter with Legolas, he can shoot them both at the same time). He will run away after a certain amount of time, and more Mumakil come. Look for which side they are on and kill it accordingly. 
The level ends when you swat the Witch King out of the air. The sooner you do it the better, for then he and the Mumakil will start coming together which can be really annoying. Give the Witch King priority. When he falls, Eowyn will stick a sword in his face and everyone wins!

The Black Gate
It seems that Gollum canít take a hint. All you have to do on this level is to kill him. But Gollum is not like any other boss youíve come across in the game: with all the others, you could simply hack them to pieces. If you try this on Gollum, it will only give him something to complain about next morning. It doesnít work.  
In addition, there will be lava and rocks falling onto the playing area while you work, so make sure to avoid them. It is easy to see where the lava is coming, because there is a red light and a few sparks. If this is over you, evacuate immediately. 
The best thing to do is to wait at the edge of the playing area. All your companion does is slow him down while you get into position. When Gollum comes close and looks like heís got constipation, heís about to jump at you. Quickly move, and he will land at the edge, hopefully teetering on the edge. If not, just hack him a bit until he is. Push him off with the X button, but the persistent little freak will cling on. Press R to stab down and send him tumbling. Repeat until dead.