Her Interactive's Nancy Drew games have been great for me.
With a mixture of puzzles, academic skills (ex. Morse Code, Shorthand) and adventure, these point and click mystery games are increadibly engaging to play with a small group of people, or perhaps just yourself.
I've been slowly purchasing all of HI's Nancy Drew games and playing each of them with my younger sisters, and with each game having it's own enviromental setting, puzzles, skills, easter eggs, game mechanics, jokes and characters, it has been a very enjoyable series that I will continue to endulge in.
It is worth noting that, in my opinion, the series has gotten stronger as Her Interactive have continued to get better.
If you plan to only get a single game in the series for now, try starting with a later game. The puzzles in Secrets Can Kill are not as refined as those in the other games in the series I've played, but it isn't to say I didn't enjoy the game.
I strongly recommend the series.