This is a mission I keep coming back to because it's just plain fun.

You have to sneak into a mansion to recover a valuable parcel that was stolen from you, and discover why it was taken. This is a simple but effective objective, and sets the mission up nicely.

The atmosphere of the mission is nice too. The snow falling outside and the warm, reddish textures used inside make the mansion seem cozy, so that it's pleasant to walk around inside.

The guard patrols are well set up; you have to stay alert but patience and observation are rewarded. This is a difficult thing to get right- often it's either trivially easy or annoyingly arbitrary- but this mission gets the balance right.

The Parcel may be small- it's just one mansion with barely a dozen rooms- and it is probably primitive by today's standards. But it has everything you need from a mission: lots of loot, guards that are fun to evade, hidden secrets, and a mystery to unravel.