Well, Maniac Mansion was not exactly the starter of this entertaining genre, Mystery House or Labyrinth came out way before. However, it represents the breakthrough and made these brainteasers popular among millions of gamers.
So what exactly made games like Maniac Mansion, Monkey Island or Zak McKracken so interesting and long-lasting? In my opinion, besides a good story, the interactive gameplay and controls. As you can see in the picture below, the player could choose from a number of actions and combine it with objects and other characters.
... the story
Two decades ago, a large Meteor hit the garden of family Edison and left a large crater. Since then, Dr. Fred, Nurse Edna and their son "Weird Ed" have become even more reclusive and strange. Patients disappear without traces. After a local teenager has been kidnapped, her boyfriend and six other friends decide to bring her back. You start your adventurous journey in front of an old, creepy mansion.
... the gameplay
As mentioned above, Maniac Mansion has a very rich story and even multiple endings. You decide your way before you even begin to play by picking the characters you want to play with. Each one has different abilities and can be useful in one or another way. It is of course possible that your characters die, which results in a game over. Mentionable is the numerous amount of red herrings and inside jokes, that always keep the game exciting. The puzzles can be quite a thrill too.
Now start playing today... but let me give you a quick warning before you begin: Do not microwave the hamster. I warned you! ;-)