The last Nancy Drew game I played was quite a few years back. That being said, I was excited when I saw there were ND games compatible for Mac on Steam! Playing Deadly Device was very fun. There were additions that I don't remember being in the previous (old, old) games (Task Bar, Hints) that made it slightly easier when stumped on what to do next. I found the game to be long, definitely your money's worth, although if you were to play it again in the near future I feel you would remember the order of events and solutions to puzzles. It may not be a game you can play mutltiple time without an adequate break in between play throughs.
The graphics were great (this game is one of Her Interactive's more recent releases) and the story line well thought out. I am a science person, so I was pleased when there were a few elements of physics/computer code needed to complete puzzles. That being said, the puzzles might not be the most fun (compared to other Nancy Drew games) if you don't like sciency things. (Not to be interpreted as if you don't have any knowledge of science you can't play this game and complete the puzzles).
Overall I enjoyed the game and I'm looking into getting another ND during the holiday sale.