The Ultimate Haunted House places the player in the middle of a bizarrely humorous and eerie haunted house populated by Wilson's wacky characters. The player must explore 13 rooms and find 13 hidden keys before 13 hours on the mystery clock run out.

Gameplay consists of interacting with the a cast of ghoulish residents who populate the house and move about it, and in collecting and exchanging an inventory of items with them. All of the main characters, as well as the house itself, contain artificial personalities that react to the actions of the player; the moody characters and the opportunity to explore the house in any order creates near-infinite replayability. Dozens of activities and puzzles embedded in the game also have consequences. These activities include a monster assembly lab, monster movies in the screening room, cooking a concoction in the kitchen, composing an organ tune, and other traditional puzzle games adapted to the computer. The game contains many clever voices and the opening tune "Monster Mash".

The following is a block of promotion copy for the game:

Come join the cast of characters in Gahan Wilson's The Ultimate Haunted House. Enjoy wandering through the 13 mysterious rooms and participating in wacky activities. You will meet weird characters and maybe even make one yourself. Try baking with your favorite disgusting ingredients in the kitchen and visit the dancing cockroaches in the bathroom. Take a break and watch TV or one of the movies. But don't forget to find the 13 keys and escape... or you may be trapped in the house forever!

A cast of characters populate the house and make appearances throughout in the game. These include Frankenstein, a vampiress, a two-headed monster, a mad scientist, and a kid (transported there by the mad scientist's lab ray). Gahan Wilson is a ghost in the game, but there are two Gahans: one good, one evil, and deciphering which is which is one of the elements of game play. The thirteen rooms include a menagerie, kitchen, foyer, torture chamber, the monster lab, the screening room, the game room, a library, an attic, a bathroom, a basement hallway, a music room, and an art gallery. There are also a variety of monsters whose interaction with the player is limited to placing curses upon them.