I started buying the manga in my local shop because I liked the art style. At the beginning I was a little skeptical. It had quite the "girly" touch to it.
After Volume 13 I was already trying to sell all the books I bought because I just didn't like the series anymore. But lets get to the rating.

STORY
The story is somewhat plain. We have that strong organisation which dedicated itself to the security of all the people in the country and also to investigate strange occurrences.
Although all the fighters of "Circus" are strong, they don't emit the feeling of a powerful and independent force. The characters from Circus we know act too much like playful and unserious figures instead of real agents and military forces. The author can't create a bridge between these two features.
Long story short: Karneval tries to create a dangerous and threating setting. With strange creatures attacking and possessing people, with an unknown but influental enemy organisation. But still: the series fails to actually pull you into a menacing world.
For my taste the story is way too happy and funny and carefree told.

ART
The art style however is great. There's lots of details and except for some of the outfits, the men in the series don't seem too feminine. Although I thought Gareki was around 25 years old and I felt like a pedophile when he said how old he was.
HOWEVER!! As a designer.. I just can't get over the font and color choices on the cover arts. You don't smack green, handwritten font on a brown background!

CHARACTER
The characters are a little hard to understand. Nai, as a young boy who is actually a tiny (and I would say primitive) animal is understandably a little dull. However Yogi as a grown 30 somewhat year old man, acts like a 5 year old boy with problems about his own gender (not that this is a bad thing).
To me, characters like him are so unrealistic and idealistic. They are quite annoying and the only interesting thing about him, is his second personality.
About the rest of the cast: there's way too many characters in too little time. You don't have enough time to get used to them. Their features aren't really defined. One minute they're serious about everything, the next second they (literally) enjoy themselves with tea, candy and childish actions. This also contributes to the missing seriousness that Karneval is actually trying to obtain.

ENJOYMENT and OVERALL
I'm a bit torn between liking and not liking the series. Right now I am just reading the manga, so I didn't waste money on them. I hope the story gets a little darker and actually manages to create realistic conflicts and character developments.