I always thought the first assault on The Pit by a Light party was one of the best battles in the whole M&M canon. I found that the best way to do it was as follows.

First, save your game outside the door. Enter The Pit from the Hall of the Pit, stay within one step of the door, and IMMEDIATELY hit Return to enter turn-based mode. Use your spellcasters to cast Paralyze on the nearest Queen of the Dead until she freezes. (If it takes too long and she is able to cast Pain Reflection, reload your position and try again.) Concentrate on her with ranged spells until she drops. You'll probably have to run and heal once the first one dies - staying so near the door enables you to turn and open it without leaving turn-based mode. If you try doing this in real-time play, your party is liable to get destroyed from behind before you can leave. Rest, return, and repeat the treatment with the rest of the QotD until all within reach are dead, then turn your attention to the Power Liches - Destroy Undead is useful here. Once you have cleared the immediate area of those, you can take the others - this will be easy in comparison, and you will then be able to move away from the door in comparative safety.