Karneval is a very original and interesting story filled with many fun moments, you cannot help but become intrigued by the plot-line and the wonderful characters surrounding it. The characters are all interesting in their own ways with their strengths, personalities and even flaws.
The only let down you may have with Karneval is that it can become confusing and difficult to understand in some places (Aka; explanation points) although most people will probably get the gist of it.
If you plan to watch the anime instead (or after reading the manga) you I say go ahead! The anime is almost exactly identical to the manga, which is a huge bonus in my books. Although the manga is much further in to the story as to be expected.