One thing that I have never felt Dungeons & Dragons has handled well are large battles fought by armies. D&D gets the details down for one-on-one combat and small scale party based encounters. The mechanics are designed to accommodate these scenarios. Unfortunately, the rules that make small scale encounters fun simply don’t translate to larger battles.
Fortunately, these types of encounters are few and far between. Most adventurers spend their time in dungeons or completing quests that don’t require armies. However, every once in a while an army is needed. We can see examples of this when we consider the Lord of the Rings. For the majority of the tale the Fellowship journeys forth as a small group. It is only during a few climactic moments that large scale battle is called for.