I played this mission many times in the past days it has replay value and i liked it much. The stats are the following: Expert difficulty - total time: 5 hr 28 min 0 sec, loot 4305 out of 4850.
Architecture: This is a high quality mission, with impressive architecture. It reminds me of "Into the Odd" in many aspects. Mixing Thief1 textures with Thief2 ones was a great idea resulting in a combined old and new fell about the place. The level of detailing is great, object placement and object richness are top class. Overall this may not be as good as "Into the Odd" in terms of quality but it's close.
Gameplay: Gameplay is puzzle based with the difficulty of the puzzles being low to medium. Also the gameplay may be pretty long or short depending on how fast you are able to solve the various puzzles. The mission consists of a few small zones linked to each other: a mansion, a lava cavern, a cave, some outside ruins and a small winter area full of stone golems. The mansion is not guarded by humans but by walking statues which freeze when you look at them - a cool new idea never seen until now. They only move when you turn your back to them which i find it's fun and adds to the mysterious atmosphere of the place. Overall the gameplay is fun and entertaining, loot is not hard to find.
Story: The story develops around a test spell which Michael, Malazar's apprentice, is left to solve by his master in his absence. When Garrett visits the place both of them are dead so he finds himself alone in a strange mansion only in the company of indestructible statues. You have to be careful to read the scroll about the test spell otherwise you will not be able to understand fully what you are supposed to do in this mission.
Atmosphere: Atmosphere is great, you are in a surreal well designed mansion, surrounded by magic. You are often teleported from one place to another. Some places are reminiscent to "The Sword" mission in TDP.
Overall this is a great mission which i highly recommend to everyone.