I haven't played the game yet, but I've watched my brother play. He got absolutely overwhelmed at Helm's Deep, and it turned out exactly like the book/movie. He had to withdraw his heroes/few remaining troops to the innermost keep, and the reinforcements showed up just in time. Very cool to watch.
In contrast, the Pelennor was a bit of a disappointment; he was able to completely repel the attacks. Would have been much cooler if the Mordor forces had breached the city. As it was, the gate fell only after he had moved his armies out onto the battlefield. Picture this: a lone troll and a few orcs walk through the gate, into a completely deserted city, and look around, completely confused.
