The game is divided into four acts. Because of the game's non-linearity, some people may finish Act I sooner than others. There are a few actions that can still be completed in Act II if you (i.e. Lewton) didn't complete them before triggering the cutscene that ends Act I. (I think this is my third or fourth replay of DN, and each playthrough was slightly different.)
AnneS, don't be concerned about the relative ease of Act I. (It just means you're a veteran adventure gamer, being thorough with the dialogue and knowing what to use where!
) Without spoiling it too much for anyone playing for the first time (or those who have not replayed in years), Lewton will also get to "connect the dots" in his investigations, and this is where DN's unique gameplay comes into effect.
I'll be back with comments about Act I. Can't wait to get on with Act II!