I was really disappointed, as well. I took as much time playing the mystery as possible because fleshing out stories and making up my own character backgrounds and motives (outside of the ones that the game provides) is just my playing style. However, I felt that it was too sterile to want to extend it any longer than I did. I played it for about 22 hours, I believe.
The problem is that the story doesn't feel fleshed-out. I most definitely did not have my expectations too high; lore at the same level of a Sims 3 lot description, for example, would have been just fine with me. They definitely could have played up the characteristics of the town, fleshed out some ideas, and made it fun and quirky -- which is the very point of the game pack.
When The Sims does fun and quirky, they are able to do it well. Their entire franchise is proof of this. Since this isn't for realistic simmers, I thought these elements would be played up; everything that occult/creepy simmers enjoy should have been amplified. New content should have reflected the town and the scenario, yes, even just for a game pack.
The execution just felt poor to me. It's lacking in many ways, the biggest one being character. :(