Big rooms should use the ‘shortsighted’ level flag, which prevents monsters from homing in on the player from far away and would make it a bit more interesting than having all the monsters converge on the player once they arrive there.

Big Room variant that has a river cutting the level in half horizontally, with a bridge across it in the center. The upstairs is placed somewhere on the left; the downstairs and all the monsters generated with the level are placed on the right. The bridge sides could be walled.

In the Big Room variant that has squares of light and darkness, make the lit regions circular rather than square (possibly by scattering candles and lanterns on the ground, or just by making random circular spots of light).

Guarantee the Big Room in all games, and possibly expand the range of levels in which it can generate.

A Big Room variant that is an idyllic scene with a nice river cutting through it with some scattered trees and maybe a couple fountains and a lake. Idyllic except for the usual bunch of monsters, of course.