What draws you to this mission is likely the beautiful Venetian aesthetic. It looks great and really gives you a change of scenery. Its gameplay is not that engaging, however.

The Ashen Age is one of the few missions in which you are prohibited from knocking out most guards, similar to how it's done in Thief II's "Framed". Since this mission requires you to mostly go back and forth through the map in search of clues (often rethreading the same path multiple times), this prohibition is a lot less engaging than it was in the aforementioned level. It frankly gets a bit tedious. This mission would have been better off without knockout restrictions.

The rest of the gameplay is alright. You're searching the area for clues about missing Keepers involved with guarding the infamous Book of Ash (see Thief I's Mage Towers, Thief II's Life of the Party, and the later missions in The Black Parade). It's pretty fun to go around and unravel the mystery as you go. It is likely the strongest point of the mission. The level design is pretty alright, but not that interesting.

It's a nice warmup for the superior "The Cinder Notes."