There are too many encounters per quest.
This is a problem because spellcasters run out of spells faster than fighters run out of hitpoints. I have observed that an adventuring party with more fighters than spellcasters does much better than an adventuring party with more spellcasters than fighters.
Currently, Escape from the Underdark favors fighters over spellcasters because of the sheer number of encounters per quest. But in the Forgotten Realms, spellcasters dominate Toril.
The reason why fighters stay useful is because not everyone can become a spellcaster. Some of the most faithful men never become clerics, while some of the most intelligent people never become wizards.
Also, fighters are there to help spellcasters conserve their spells. If an adventuring party runs into a group of unskilled bandits, the fighter can take them out without having the wizard waste his Fireball.
The fighter should never be the dominant force in the party. However, he should still play a very important role.
Of course, a fighter still needs a wizard. A fighter cannot bypass a wererat's damage reduction and will eventually die. A wizard can kill a wererat one on one, but he will have to use up all of his magic to do so. A fighter working with a wizard can defeat a wererat by having the wizard cast Magic Weapon on the fighter's weapon.
The problem gets even worse once clerics come into play.
A cleric can fight almost as well as a fighter. In Escape from the Underdark, he can defeat most low-level enemies without using his magic. When he runs into more powerful foes, like wererats, he simply casts Magic Weapon on his spear/mace/morningstar/whatever and pwns the wererats.
A party made up of only clerics can accomplish a lot more than a mixed party of fighters and wizards.
Unfortunately, this is a problem with the game system itself, not just Escape from the Underdark. The cleric is the most powerful class in D&D 3.0 and 3.5.
Which brings me back to my original point. Wizards should be more powerful than fighters.
Here is one possible solution. When an adventuring party enters hostile territory, every hostile creature immediately rushes towards them. This will make area of effect spells more useful, making wizards more useful.
The Underdark tactician knows that if he sends too few troops against a threat, he will end up losing them without accomplishing anything. He also knows that if he sends too many troops, he will suffer more casualties from spells like Fireball, but will have a higher chance of inflicting casualties on the enemy.
Either way, he loses troops, so to cut his losses, he'll most likely go with the latter, which gives him a chance to inflict some damage on the enemy.
This should not happen in every quest or wizards will become too dominant. A little variety will be very nice.
Rogues are weaker than fighters, clerics, or wizards, but they keep these three from losing too many hitpoints unnecessarily. Rogues can scout ahead and tell the party what to expect. Rogues can disarm traps. Rogues can pick locks.
Rogues are currently balanced in Escape from the Underdark.
That's all for now. What do you think?