I like it as is. I also think it wouldn't hurt to make the gameplay more challenging and/or to advertise packs as optional elements that make the game more challenging on purpose if you want an extra challenge (like vampires). And then make those packs really kinda hard.
In the beginning I felt that the better I got at playing the game, the more freedom I had to tell the story I wanted. The gameplay and sandbox help each other in that way. The only disadvantage is that it didn't take long to get good at the game.