Very good.
The whole story was alright, the voice acting and animation of the characters was amazing, and the puzzles were a lot of fun. I know that all nancy drew games are a little confining since you can only go to certain places and need to move around in certain ways to see a clue, but the game as a whole was very enjoyable. You even get to play as Bess, Nancy's friend.
You can probably finish the whole game in a day if you use a walkthrough for the tougher puzzles. The 'mystery' in the game is very well done since you really don't (I didn't) know who the villian is until the last fifth of the game.
The voice acting is very funny and brings the characters to life. All the cutscenes are beautifully done and the game even has a checklist for all the quests at junior detective level; a handy feature.
The game isn't as exciting as an action game, but it's made more for the casual gamer.