René said:
Coming back to the initial question: can please someone give a few lines, e.g. about difficulty, probability of the plot, "sorcery level" etc.?
Difficulty: I played it with a group of 6th level characters and it was appropriately difficult. It was designed for four to six players of 5th to 7th level.
Probability of the Plot: Mostly probable. The least probable element is when Publius "hires" the characters to do further investigating in Chapter 2 - for all he knows, he is hiring complete bumblers. When I played it, my players pretty much asked for the job, so this "asking" on the part of Publius didn't occur. My players talked him into it. The rest of the plot is highly probable.
Sorcery Level: Appropriate.
Railroad Level: Low. My players did a few things out of order, which did not affect the playability at all, so the adventure was not straight-jacketed or railroaded like some modules tend to be. The most obvious rail-roading element was the encounter with Publius, but my Players were already interested in solving the mystery because of the strong hook, so they felt like they railroaded Publius.
Hook Quality: Among the best. It hooked my players from the start.
All in all: It was FAR above the average and a lot of fun to play.