There are a couple of really evil points in the game, which are either pretty hard (however, this can mostly be remedied by tricking the AI), or just very puzzling.
For instance, I think I've seen 4 or 5 people ask how to lower that bridge in the last two days. Another IMO very difficult scene is the one in that restaurant (people who were there will know what I mean), as was the self-destructing base. The last puzzle is also pretty hard - I spent about half an hour reloading and trying, and so did a friend.