I'd recommend all the Lucas Arts adventures except maybe Maniac Mansion, Zak McKraken
What? You evil bastard, don't destroy my childhood memories!
Maniac Mansion was a pretty special game, weird setting and story, but though very easy to solve (multiple endings) versus other point&click games of that era.
Zak McKraken however, definitely in my top 5 of adventure games, that game was and is still hilarious, excellent puzzles and problem solving, you can actually fail by using things wrong leaving you stuck, not easy to complete.