I'll provide my SPOILER-FREE review in brief, bulleted format. Keep in mind that I haven't run this adventure, but I read it with running it in mind. I did play in a very abbreviated version as part of this year's Roll20Con.
Carnival of the Damned is a tremendous value for the money. It contains 130+ pages of content including dozens of very clever magic items and a well-developed patron.
While it would be great fun for a tournament, it would really shine as the start to a campaign. Don't rush through this adventure. The author is absolutely correct that this adventure is best enjoyed as a zero level funnel with no time constraints.
The adventure would require multiple sessions to progress through all of the content and achieve the end goal. To do it justice, do not attempt it as a four-hour one-shot.
It is probably necessary to level up at least once to be successful as the encounters are very challenging, and many are quite deadly.
As judge, put some effort into ensuring that the players get bits and pieces of the background so that they can understand the underlying story.
The author makes good use of the die chain, something i haven't seen employed as frequently elsewhere.
If I had to criticize (and I don't feel that I do), I would suggest that you develop your own, longer paraphrased descriptions for each encounter. Out of necessity, the descriptions are a bit briefer and less descriptive than they could be. Likewise, you may wish to develop maps and/or illustrations for some of the encounters without them.
[5 of 5 Stars!]