The player explores sixteen dungeon levels beneath Tristram from an overhead perspective. Each level contains monsters, treasure, doors, environmental obstacles, and occasional quests, with layouts and enemy placements generated for a new game.

Combat is performed in real time with weapons, spells, and class abilities. The Warrior emphasizes melee, the Rogue favors bows, and the Sorcerer specializes in magic. Experience raises character level and grants attribute points, while equipment, gold, spell books, and scrolls provide most of the moment-to-moment progression. The objective is to reach the lowest level and defeat Diablo.

Upgrade equipment regularly and keep spare weapons, armor, and healing supplies in town. Identify unidentified items before relying on them, and use town trips to repair gear and manage inventory.

Explore cautiously, draw small groups of enemies into favorable positions, and use doorways or corridors to limit how many monsters can attack at once. Match the character class to its strengths: melee durability for the Warrior, distance for the Rogue, and spell selection plus mana management for the Sorcerer.