Denethor is a rather unique hero. Firstly, he doesn't gain levels - he stays fixed at Level 5 when you train him - after all, he is rather stangnant in his ideals. This doesn't mean that he's any less a force to be reckoned with, however. He remains the only hero with a retinue - when trained, he is surrounded by four Guardsmen, who will attack enemies if the Steward so requires. He himself will hang back and observe. If they die, they will be replaced after a short duration.
His abilities are also somewhat unique - many of them have disadvantages as well as advantages. He can gaze into the corrupted palantir of Minas Tirith, revealing an area, but at a cost to his own sanity. After such an undertaking all of your troops on the map will be debuffed for a short while, so take when you use it. His Shrewd Leader aura is also a double-edged sword: it provides bonuses to attack and armour, but decreases experience gain and fear resistance. As a counterbalance, he does have a powerful experience-granting ability, Steward's Favour, which is more powerful than others in the game. His most unappealing attribute though is his tendency to see others as a threat to his kingdom. Last of His House passively damages 'threats' that are nearby - these threats are Aragorn and Gandalf. Though the damage is low compared to large health values, it adds up over time, so Denethor should not be placed idly near either of them, lest he undermine their efforts to save Gondor from the Dark Lord.
Pippin is a much more cheerful character. He keeps his Throw Rocks/Draw Sword toggle, and gains two new abilities. At Level 4, he dons his Citadel armour, getting a substantial armour bonus. At level 5, he gains the passive Trollsbane, an ability that greatly increases his damage against Trolls.
Edited by Nertea, 19 April 2011 - 11:43 PM.