Alone in the Dark is an action-adventure survival horror game. The action is displayed from a number of fixed viewpoints. The backgrounds are 2D painted images, while the player character, all items and monsters are rendered as 3D models.
To escape the mansion, you'll have to solve a number of puzzles. They usually involve finding an item and using it in a proper place. Apart from items necessary for the puzzles, you can also find books and documents that can be read, healing items which can be consumed to restore hit points, and weapons.
Weapons come in handy, since Derceto is full of various monsters. Some monsters can be killed with weapons, but others are either impossible to kill or require a bit of thinking to take down. Note also that you have limited amounts of ammunition, so you have to use firearms carefully.